Showing 1–50 of 70 results for author: Dias, A

Chemical Control of Electronic Structure and Topology in Tellurium-Encapsulated Silicene

Authors: Gabriel Elyas Gama Araujo, Andre Luis de Oliveira Batista, Willian Oliveira Santos, Alexandre Amaral Leitao, Alexandre Cavalheiro Dias, Andreia Luisa da Rosa

Abstract: We investigate chemical control of the electronic, optical, and topological properties of two-dimensional \ce{Si2X2Te2} (\ce{X} = \ce{B}, \ce{Al}, \ce{Ga}, and \ce{In}) monolayers using first-principles calculations. All compounds are dynamically stable semiconductors, with their vibrational and electronic properties evolving systematically upon group-III substitution. Hybrid-functional calculatio… ▽ More We investigate chemical control of the electronic, optical, and topological properties of two-dimensional \ce{Si2X2Te2} (\ce{X} = \ce{B}, \ce{Al}, \ce{Ga}, and \ce{In}) monolayers using first-principles calculations. All compounds are dynamically stable semiconductors, with their vibrational and electronic properties evolving systematically upon group-III substitution. Hybrid-functional calculations including spin--orbit coupling reveal predominantly $p$-orbital band edges and increasingly pronounced relativistic effects from B to In. Most notably, the calculated $\mathbb{Z}_2$ invariant identifies \ce{Si2In2Te2} as a candidate quantum spin Hall insulator, while the B-, Al-, and Ga-based monolayers remain topologically trivial. Bethe--Salpeter calculations further show that electron--hole interactions redistribute oscillator strength near the absorption onset while preserving a weak in-plane optical anisotropy. Our results establish group-III substitution as a simple chemical route to tune the electronic structure and drive a transition from trivial to nontrivial topology in \ce{Si2X2Te2} monolayers. △ Less

Submitted 21 August, 2026; originally announced August 2026.

Instability-induced bistable shape-morphing kirigami structures

Authors: Xiaoyuan Ying, Marcelo A. Dias

Abstract: Deployable shape-morphing structures that transform from flat sheets into stable three-dimensional configurations are highly desirable for applications ranging from soft robotics and biomedical devices to adaptive architecture and aerospace systems. Existing kirigami-based morphing systems primarily rely on isotropic deployment, compliant soft materials, or external constraints to maintain deploye… ▽ More Deployable shape-morphing structures that transform from flat sheets into stable three-dimensional configurations are highly desirable for applications ranging from soft robotics and biomedical devices to adaptive architecture and aerospace systems. Existing kirigami-based morphing systems primarily rely on isotropic deployment, compliant soft materials, or external constraints to maintain deployed shapes, which limits geometric programmability, structural integrity, and applicability in rigid-material systems. Here, we present an inverse design framework for anisotropic bistable kirigami structures that enables programmable shape morphing through controlled geometric frustration and instability-induced deployment. The framework combines a semi-analytical mechanical model with geometry to establish a direct connection between geometric transformation and the underlying energy landscape. We show that instability-induced shape morphing leads to tunable bistability and directional deployment in anisotropic kirigami structures. The results are validated through finite element simulations and experiments, demonstrating stable deployed configurations and programmable anisotropic morphing. The proposed framework further provides a general design strategy that can be integrated with various active actuation systems, enabling broader engineering applications. △ Less

Submitted 29 July, 2026; originally announced July 2026.

Nonlinear Mechanics and Predictable Bifurcation of Multi-Cell Kresling Origami Chains

Authors: Songlin Yue, Leo de Waal, David Garcia Cava, Marcelo A. Dias

Abstract: Meta-structures that display axial-twist coupling can be achieved through the emerging kinematics in Kresling origami patterns. A central challenge in these structures is understanding their nonlinear mechanical behaviour, specifically their equilibrium branches and bifurcation diagrams. This involves identifying relationships between desired responses and the geometric variables that define the d… ▽ More Meta-structures that display axial-twist coupling can be achieved through the emerging kinematics in Kresling origami patterns. A central challenge in these structures is understanding their nonlinear mechanical behaviour, specifically their equilibrium branches and bifurcation diagrams. This involves identifying relationships between desired responses and the geometric variables that define the design space, including the Kresling polygon count, initial twist angle, height, radius, and crease lengths. As the number of constituent units increases in an n-layer chain, we track complex equilibrium branches extending into the post-critical regime under successive instabilities, including branch-point bifurcations and limit-point instabilities. This work begins by establishing the relationship between the geometric design variables and the response curves of the assembled chain by modelling the crease lines as axial-load-carrying elements. Subsequently, equilibrium branches and instabilities are systematically investigated via continuation and bifurcation analysis, beginning with the single-layer system and progressively extending to two- and three-layer configurations. Finally, a generalisation strategy is proposed to extend these findings to an n-layer Kresling chain. This strategy enables the predictive construction of equilibrium paths and the inverse design of multi-layer meta-structures, using prescribed critical points to control post-critical behaviour. It provides a foundation for the inverse design and optimisation of architected mechanical metamaterials with programmable responses. △ Less

Submitted 10 June, 2026; originally announced June 2026.

Mean-Field Theory for the Three-State Active Lattice Gas Model

Authors: Ana L. N. Dias, Ronald Dickman, Tiago Venzel Rosembach

Abstract: We develop a mean-field description including spatial structure for a simplified version of the three-state active matter model studied by Venzel et al. (Phys. Rev. E 110, 014109 (2024)). The resulting triangular lattice of coupled nonlinear differential equations are integrated numerically using a fourth-order Runge-Kutta scheme. Starting from various ordered initial configurations, we probe the… ▽ More We develop a mean-field description including spatial structure for a simplified version of the three-state active matter model studied by Venzel et al. (Phys. Rev. E 110, 014109 (2024)). The resulting triangular lattice of coupled nonlinear differential equations are integrated numerically using a fourth-order Runge-Kutta scheme. Starting from various ordered initial configurations, we probe the stability of the corresponding stationary states, revealing the presence of various high-density ordered structures in the density(\r{ho})-noise(η) plane. The results are compared with Monte Carlo simulations of the simplified model, yielding, in certain cases, unexpected transitions between ordered configuration types. △ Less

Submitted 24 April, 2026; originally announced April 2026.

Comments: 34 pages, 20 figures

Exciton dynamics and high-temperature excitonic superfluidity in S-doped graphyne

Authors: Enesio Marinho Jr., Alexandre C. Dias, Luiz A. Ribeiro Jr., Maurizia Palummo, Cesar E. P. Villegas

Abstract: S-doped graphyne (S-GY) is a recently synthesized two-dimensional graphyne-based carbon allotrope that provides a promising platform for exciton engineering and coherent many-body phases. Here, we investigate the quasiparticle electronic structure, optical response, and exciton dynamics of monolayer S-GY using the G$_0$W$_0$ approximation and the Bethe--Salpeter equation (BSE). Quasiparticle corre… ▽ More S-doped graphyne (S-GY) is a recently synthesized two-dimensional graphyne-based carbon allotrope that provides a promising platform for exciton engineering and coherent many-body phases. Here, we investigate the quasiparticle electronic structure, optical response, and exciton dynamics of monolayer S-GY using the G$_0$W$_0$ approximation and the Bethe--Salpeter equation (BSE). Quasiparticle corrections increase the fundamental band gap from $0.88\,\text{eV}$ (PBE) to $1.95\,\text{eV}$, while slightly reducing the carrier effective masses. The BSE optical response reveals strongly bound excitons, with the lowest bright exciton exhibiting a binding energy of $0.72\,\text{eV}$, as well as a nearly degenerate dark exciton within the thermal energy scale. Analysis of exciton wavefunctions in reciprocal space confirms a hydrogenic Rydberg series with well-defined angular-momentum character, and radiative lifetimes in the nanosecond range at room temperature, comparable to those in transition-metal dichalcogenide monolayers. Finally, we construct the excitonic phase diagram and estimate a crossover density of $\sim6 \times10^{12}~\text{cm}^{-2}$, below which the exciton gas behaves as a dilute Bose system, and the Berezinskii--Kosterlitz--Thouless (BKT) superfluid phase becomes accessible. We estimate a maximum BKT transition temperature of $\sim 143\,\text{K}$ in the freestanding limit for the 1s exciton, indicating that monolayer S-GY may provide favorable conditions for high-temperature excitonic superfluidity in graphyne-based materials. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Qudit Implementation of the Rodeo Algorithm for Quantum Spectral Filtering

Authors: Julio Cesar Siqueira Rocha, Rodrigo Alves Dias

Abstract: Qudits, the multi-level generalization of qubits, provide a natural extension of the binary paradigm in quantum computation and offer new opportunities to enhance algorithmic performance. Beyond their direct applicability to the simulation of multi-level quantum systems, higher-dimensional ancillae can improve sampling efficiency in quantum algorithms by enabling the simultaneous implementation of… ▽ More Qudits, the multi-level generalization of qubits, provide a natural extension of the binary paradigm in quantum computation and offer new opportunities to enhance algorithmic performance. Beyond their direct applicability to the simulation of multi-level quantum systems, higher-dimensional ancillae can improve sampling efficiency in quantum algorithms by enabling the simultaneous implementation of multiple control operations, thereby reducing circuit complexity. In this work, we pursue three main objectives. First, we present a formulation of the Rodeo algorithm employing a general $d$-level ancilla qudit. Second, we introduce the concept of the \emph{Rodeo kernel}, defined as a two-frequency interferometer, which acts as a spectral filter in the energy domain. Finally, we propose a microcanonical protocol for the Rodeo algorithm. This protocol enables the estimation of entropic quantities through a single energy sweep and admits a natural interpretation as a Gaussian convolution of the density of states. To support the theoretical analysis, we perform numerical evaluations of the corresponding quantum circuit using ancilla qudits of dimensions three, four, and five. The simulations are performed for the one-dimensional Ising model, considering both spin-$\frac{1}{2}$ and spin-$1$ particles. The ancilla qutrit implementation exhibits an $18\%$ reduction in fluctuations compared to the qubit implementation. Our results show that the qudits provide a framework for spectral analysis and thermodynamic characterization of multi-level quantum systems. △ Less

Submitted 16 March, 2026; originally announced March 2026.

Comments: 19 pages, 6 figures

Chalcogen Impurity Barriers in 2D Systems via Semi-Empirical/Machine Learning Modeling: A Survey over 4000 Materials

Authors: M. L. Pereira Junior, M. G. E. da Luz, P. Cesana, A. L. da Rosa, M. J. Piotrowski, D. Guedes-Sobrinho, T. A. S. Pereira, E. A. Moujaes, A. C. Dias, R. M. Tromer

Abstract: Adequate characterization of two-dimensional materials with low energy barriers for impurity adsorption is key for advancing applications based on catalysis, sensing, and surface functionalization. However, first-principles methods, such as DFT, are often computationally extremely expensive for feasible large-scale screenings. Given such a scenario, we address a data-driven approach which integrat… ▽ More Adequate characterization of two-dimensional materials with low energy barriers for impurity adsorption is key for advancing applications based on catalysis, sensing, and surface functionalization. However, first-principles methods, such as DFT, are often computationally extremely expensive for feasible large-scale screenings. Given such a scenario, we address a data-driven approach which integrates the semi-empirical Extended Huckel Method with machine learning techniques to estimate adsorption energy barriers in the case of three relevant chalcogen impurities, S, Se and Te. With this aim, we consider the 4036 2D materials found in the C2DB. The scheme employs the EHM to compute energy profiles along three in-plane migration paths, from which average barriers can be derived. The equilibrium distance between the impurity and the 2D surface is not calculated from a tie-consuming geometry optimization. Instead, it is estimated from a simple effective phenomenological expression. Physicochemical descriptors are then obtained from the Matminer library for curated features. Four different ML models are tested, with the XGBoost leading to the highest performance. We further use SHAP to verify the resulting predictions, focusing on the $\sim1,500$ materials displaying the lowest barrier values. As it could be anticipated, we establish that the average valence electron count, electronegativity, and atomic number are typically the most relevant attributes to validate the ML model. But we also are able to determine, for the different chalcogen atoms, which other few descriptors likewise considerably influence the adsorption properties. Our results show that when combined with interpretable ML protocols, EHM can produce a scalable framework for choosing 2D structures that exhibit the desired capture/release dynamics pertinent in a variety of utilization. △ Less

Submitted 26 February, 2026; originally announced February 2026.

Comments: 25 pages, 09 figures

MSC Class: 00-xx ACM Class: J.2; I.6

Phase-Dependent Excitonic Light Harvesting and Photovoltaic Limits in Monolayer Y2TeO2 MOenes

Authors: Bill D. A. Huacarpuma, Jose A. dos S. Laranjeira, Nicolas F. Martins, Julio R. Sambrano, Kleuton A. L. Lima, Santosh K. Tiwari, Alexandre C. Dias, Luiz A. Ribeiro Jr

Abstract: We investigate phase-dependent electronic and excitonic phenomena in monolayer Y2TeO2 MOenes in the 1T and 2H polymorphs using first-principles theory and an effective many-body framework. Phonon spectra and elastic stability criteria establish both phases as dynamically and mechanically stable. Quasiparticle band structures reveal direct gaps in the near-infrared to visible range, with gap values… ▽ More We investigate phase-dependent electronic and excitonic phenomena in monolayer Y2TeO2 MOenes in the 1T and 2H polymorphs using first-principles theory and an effective many-body framework. Phonon spectra and elastic stability criteria establish both phases as dynamically and mechanically stable. Quasiparticle band structures reveal direct gaps in the near-infrared to visible range, with gap values increasing systematically from semilocal to hybrid exchange treatments. Optical spectra computed using a tight-binding Bethe-Salpeter approach demonstrate pronounced excitonic resonances arising from reduced dimensionality and weak dielectric screening. The exciton binding energies reach 152 meV in the 1T phase and 126 meV in the 2H phase, reflecting enhanced quantum confinement in the structurally denser phase. Our results identify Y2TeO2monolayers as a rare class of stable, direct-gap MOenes with strong excitonic effects, providing a platform for exploring many-body physics in low-dimensional oxychalcogenide systems especially for photovoltaic applications. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Comments: In preparation for Journal Submission

How Geometry Tames Disorder in Lattice Fracture

Authors: Matthaios Chouzouris, Leo de Waal, Antoine Sanner, Alessandra Lingua, David S. Kammer, Marcelo A. Dias

Abstract: We investigate the fracture behavior of pre-cracked triangular beam-lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morpholog… ▽ More We investigate the fracture behavior of pre-cracked triangular beam-lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morphology, and (iii) disorder manifests globally, leading to initially diffuse failure. Our model naturally reveals the key parameters governing this behavior: the Weibull modulus, quantifying the spread in failure thresholds, and a geometric quantity termed the Slenderness Ratio. We also reproduce the disorder-induced toughening reported in previous experimental and numerical studies, further demonstrating that its manifestation depends non-monotonically on disorder. Crucially, our results indicate that this toughening cannot be simply connected to the amount of damage in the lattice, challenging interpretations that attribute increased fracture energy solely to enhanced crack tortuosity or diffuse failure. Overall, our results establish geometry as a powerful control parameter for regulating how disorder is expressed during fracture in beam-lattices, with broader implications for the disorder-induced toughening in engineered materials. △ Less

Submitted 10 February, 2026; originally announced February 2026.

Interpretable, Physics-Informed Learning Reveals Sulfur Adsorption and Poisoning Mechanisms in 13-Atom Icosahedra Nanoclusters

Authors: Raiane Ferreira Monteiro, João Marcos T. Palheta, Tulio Gnoatto Grison, Octávio Rodrigues Filho, Renato Luis Tame Parreira, Diego Guedes-Sobrinho, Celso R. C. Rêgo, Alexandre C. Dias, Krys Elly de Araújo Batista, Maurício J. Piotrowski

Abstract: Transition-metal nanoclusters exhibit structural and electronic properties that depend on their size, often making them superior to bulk materials for heterogeneous catalysis. However, their performance can be limited by sulfur poisoning. Here, we use dispersion-corrected density functional theory (DFT) and physics-informed machine learning to map how atomic sulfur adsorbs and causes poisoning on… ▽ More Transition-metal nanoclusters exhibit structural and electronic properties that depend on their size, often making them superior to bulk materials for heterogeneous catalysis. However, their performance can be limited by sulfur poisoning. Here, we use dispersion-corrected density functional theory (DFT) and physics-informed machine learning to map how atomic sulfur adsorbs and causes poisoning on 13-atom icosahedral clusters from 30 different transition metals (3$d$ to 5$d$). We measure which sites sulfur prefers to adsorb to, the thermodynamics and energy breakdown, changes in structure, such as bond lengths and coordination, and electronic properties, such as $\varepsilon_d$, the HOMO-LUMO gap, and charge transfer. Vibrational analysis reveals true energy minima and provides ZPE-based descriptors that reflect the lattice stiffening upon sulfur adsorption. For most metals, the metal-sulfur interaction mainly determines adsorption energy. At the same time, distortion penalties are usually moderate but can be significant for a few metals, suggesting these are more likely to restructure when sulfur is adsorbed. Using unsupervised \textit{k}-means clustering, we identify periodic trends and group metals based on their adsorption responses. Supervised regression models with leave-one-feature-out analysis identify the descriptors that best predict adsorption for new samples. Our results highlight the isoelectronic triad \ce{Ti}, \ce{Zr}, and \ce{Hf} as a balanced group that combines strong sulfur binding with minimal structural change. Additional DFT calculations for \ce{SO2} adsorption reveal strong binding and a clear tendency toward dissociation on these clusters, linking electronic states, lattice response, and poisoning strength. These findings offer data-driven guidelines for designing sulfur-tolerant nanocatalysts at the subnanometer scale. △ Less

Submitted 20 January, 2026; originally announced January 2026.

Journal ref: Scientific Reports 16, 14174 (2026)

Kagome Topology in Two-Dimensional Noble-Metal Monolayers

Authors: Carlos M. O. Bastos, Emanuel J. A. dos Santos, José A. dos S. Laranjeira, Kleuton A. L. Lima, Alexandre C. Dias, Douglas S. Galvão, Luiz A. Ribeiro Jr

Abstract: Two-dimensional (2D) metallic lattices with kagome topology provide a unique platform for exploring the interplay between geometric frustration, reduced coordination, and lattice stability in elemental systems. Motivated by the recent experimental realization of atomically thin gold layers and kagome goldene, we present a first-principles investigation of free-standing kagome monolayers of Cu, Ag,… ▽ More Two-dimensional (2D) metallic lattices with kagome topology provide a unique platform for exploring the interplay between geometric frustration, reduced coordination, and lattice stability in elemental systems. Motivated by the recent experimental realization of atomically thin gold layers and kagome goldene, we present a first-principles investigation of free-standing kagome monolayers of Cu, Ag, and Au. Using density functional theory combined with lattice dynamics and ab initio molecular dynamics, we systematically assess their structural, mechanical, dynamical, and thermal stability. All kagome monolayers satisfy the 2D Born criteria and exhibit relatively low in-plane stiffness compared to graphene and hexagonal goldene, reflecting the porous nature of the kagome lattice and its metallic bonding. Among the three systems, the Au-based lattice displays the highest in-plane Young's modulus. Phonon calculations reveal that the unstrained kagome phase is dynamically unstable for all metals. However, a moderate biaxial tensile strain of 5% stabilizes the Ag and Au monolayers, while Cu retains residual unstable modes. Finite-temperature simulations further show that Cu rapidly reconstructs toward a trigonal lattice, Ag remains metastable at low temperature but collapses at room temperature, and Au exhibits competing kagome and trigonal motifs at 300 K, indicating near-degeneracy between these phases. These results establish that strain engineering and atomic size are key determinants of the stability of metallic kagome monolayers and provide guidance for future substrate-supported realizations. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 10 pages, 3 figures

MSC Class: 00-XX ACM Class: I.2; J.6

GENIUS: An Agentic AI Framework for Autonomous Design and Execution of Simulation Protocols

Authors: Mohammad Soleymanibrojeni, Roland Aydin, Diego Guedes-Sobrinho, Alexandre C. Dias, Maurício J. Piotrowski, Wolfgang Wenzel, Celso Ricardo Caldeira Rêgo

Abstract: Predictive atomistic simulations have propelled materials discovery, yet routine setup and debugging still demand computer specialists. This know-how gap limits Integrated Computational Materials Engineering (ICME), where state-of-the-art codes exist but remain cumbersome for non-experts. We address this bottleneck with GENIUS, an AI-agentic workflow that fuses a smart Quantum ESPRESSO knowledge g… ▽ More Predictive atomistic simulations have propelled materials discovery, yet routine setup and debugging still demand computer specialists. This know-how gap limits Integrated Computational Materials Engineering (ICME), where state-of-the-art codes exist but remain cumbersome for non-experts. We address this bottleneck with GENIUS, an AI-agentic workflow that fuses a smart Quantum ESPRESSO knowledge graph with a tiered hierarchy of large language models supervised by a finite-state error-recovery machine. Here we show that GENIUS translates free-form human-generated prompts into validated input files that run to completion on $\approx$80% of 295 diverse benchmarks, where 76% are autonomously repaired, with success decaying exponentially to a 7% baseline. Compared with LLM-only baselines, GENIUS halves inference costs and virtually eliminates hallucinations. The framework democratizes electronic-structure DFT simulations by intelligently automating protocol generation, validation, and repair, opening large-scale screening and accelerating ICME design loops across academia and industry worldwide. △ Less

Submitted 6 December, 2025; originally announced December 2025.

Journal ref: Communications Materials 7, 115 (2026)

Teaching a Transformer to Think Like a Chemist: Predicting Nanocluster Stability

Authors: João Marcos T. Palheta, Octavio Rodrigues Filho, Mohammad Soleymanibrojeni, Alexandre Cavalheiro Dias, Diego Guedes-Sobrinho, Wolfgang Wenzel, Roland Aydin, Celso R. C. Rêgo, Maurício Jeomar Piotrowski

Abstract: Atomically precise metal nanoclusters bridge the molecular and bulk regimes, but designing bimetallic motifs with targeted stability and reactivity remains challenging. Here we combine density functional theory (DFT) and physics-grounded predictive artificial intelligence to map the configurational landscape of 13-atom icosahedral nanoclusters X$_{12}$TM, with hosts X = (Ti, Zr, Hf), and Fe and a… ▽ More Atomically precise metal nanoclusters bridge the molecular and bulk regimes, but designing bimetallic motifs with targeted stability and reactivity remains challenging. Here we combine density functional theory (DFT) and physics-grounded predictive artificial intelligence to map the configurational landscape of 13-atom icosahedral nanoclusters X$_{12}$TM, with hosts X = (Ti, Zr, Hf), and Fe and a single transition--metal dopant spanning the 3$d$-5$d$ series. Spin-polarized DFT calculations on 240 bimetallic clusters reveal systematic trends in binding and formation energies, distortion penalties, effective coordination number, d-band centre, and HOMO-LUMO gap that govern the competition between core-shell (in) and surface-segregated (out) arrangements. We then pretrain a transformer architecture on a curated set of 2968 unary clusters from the Quantum Cluster Database and fine-tune it on bimetallic data to predict formation energies and in/out preference, achieving mean absolute errors of about $0.6-0.7$eV and calibrated uncertainty intervals. The resulting model rapidly adapts to an unseen Fe-host domain with only a handful of labelled examples. At the same time, attention patterns and Shapley attributions highlight size mismatch, $d$-electron count, and coordination environment as key descriptors. All data, code, and workflows follow FAIR/TRUE principles, enabling reproducible, interpretable screening of unexplored nanocluster chemistries for catalysis and energy conversion. △ Less

Submitted 4 December, 2025; originally announced December 2025.

Flat bands in ultra-wide gap two-dimensional germanium dioxide

Authors: Rafael Franco Ribeiro Reis, Gabriel Elyas Gama Araujo, Danilo Kuritza, Alexandre Cavalheiro Dias, Andreia Luisa da Rosa, Renato Borges Pontes

Abstract: We employ first principles density-functional theory (DFT) and the Bethe-Salpeter equation (BSE) in the framework of tight-binding based maximally localized Wannier functions (MLWF-TB) model to investigate the electronic and optical properties of free-standing two-dimensional (2D) germanium dioxide phases. All investigated 2D GeO2 polymorphs exhibit ultra-wide band gaps and strong excitonic effect… ▽ More We employ first principles density-functional theory (DFT) and the Bethe-Salpeter equation (BSE) in the framework of tight-binding based maximally localized Wannier functions (MLWF-TB) model to investigate the electronic and optical properties of free-standing two-dimensional (2D) germanium dioxide phases. All investigated 2D GeO2 polymorphs exhibit ultra-wide band gaps and strong excitonic effects, with flat O-p-derived valence bands tunable under strain. These features allow the design of flat band materials with ultra large electronic gaps in low-dimensional systems, making these materials promising for devices operation at higher voltages and temperatures than conventional semiconductor materials. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Sodium-Decorated Ennea-Graphene: A Novel 2D Carbon Allotrope for High-Capacity Hydrogen Storage

Authors: Bill D. Aparicio Huacarpuma, José A. S. Laranjeira, Nicolas F. Martins, Julio R. Sambrano, Fábio L. Lopes de Mendonça, Alexandre C. Dias, Luiz A. Ribeiro Junior

Abstract: The development of safe, efficient, and reversible hydrogen storage materials is critical for advancing hydrogen-based energy technologies and achieving carbon-neutral goals. Ennea-Graphene, a new 2D carbon allotrope made of 4-, 5-, 6-, and mainly 9-membered carbon rings (nonagons), is introduced via Density Functional Theory (DFT) calculations. Phonon dispersion and ab initio molecular dynamics d… ▽ More The development of safe, efficient, and reversible hydrogen storage materials is critical for advancing hydrogen-based energy technologies and achieving carbon-neutral goals. Ennea-Graphene, a new 2D carbon allotrope made of 4-, 5-, 6-, and mainly 9-membered carbon rings (nonagons), is introduced via Density Functional Theory (DFT) calculations. Phonon dispersion and ab initio molecular dynamics demonstrate that the monolayer is mechanically and dynamically stable at 300 K, as no imaginary modes are detected. The pristine system further exhibits metallic-like electronic behavior. The material exhibits high in-plane stiffness (Young modulus of 255 N/m). Sodium adsorption at the centers of the nonagonal rings is energetically favorable, with a binding energy of approximately -1.56 eV, leading to the formation of the Na@Ennea-Graphene complex. The calculated H2 adsorption energies range from -0.15 eV to -0.18 eV. The Na-decorated structure demonstrates excellent hydrogen storage performance, reversibly adsorbing up to four H2 molecules per Na atom (8.8 wt\% H2). This capacity surpasses the U.S. Department of Energy's 2025 target for onboard hydrogen storage materials. The adsorbed H2 remains molecular (H-H bond of 0.76~Å) and can be released under near-ambient conditions, as verified by 300 K ab initio molecular dynamics simulations. These findings position sodium-decorated Ennea-Graphene as a promising nanomaterial for next-generation hydrogen storage technologies. △ Less

Submitted 23 September, 2025; originally announced September 2025.

Comments: In preparation for Journal Submission

Towards High-Efficiency Solar Cells: Insights into AsNCa 3 Antiperovskite as Active Layer

Authors: M. Irfan, B. D. Aparicio-Huacarpuma, C. M. de Oliveira Bastos, M. J. Piotrowski, C. R. C. Rêgo, D. Guedes-Sobrinho, R. Besse, A. M. Almeida Silva, Alexandre C. Dias, L. A. Ribeiro Jr

Abstract: Advances in photovoltaic technology are a viable route to contribute to cleaner and more sustainable energy solutions, placing perovskite-based materials among the best candidates for solar energy conversion. However, some challenges must be addressed to enhance their performance and stability. Herein, we report an investigation of the AsNCa3 antiperovskite system for its potential in photovoltaic… ▽ More Advances in photovoltaic technology are a viable route to contribute to cleaner and more sustainable energy solutions, placing perovskite-based materials among the best candidates for solar energy conversion. However, some challenges must be addressed to enhance their performance and stability. Herein, we report an investigation of the AsNCa3 antiperovskite system for its potential in photovoltaic devices. We consider eight distinct crystalline phases, their structural parameters, dynamical stability, and electronic and optical properties. Furthermore, we consider each structural phase's contributions to solar harvesting efficiency by calculating the power conversion efficiency (PCE) using the spectroscopiclimited maximum efficiency (SLME) formalism, which in this case reaches a maximum of 31.2%. All dynamically stable phases exhibit a band gap around 1.3 eV, which lies within the optimal range for single-junction solar cells and yields PCE values comparable to the theoretical maximum PCE for silicon. These results place AsNCa3 antiperovskites as promising candidates for high-efficiency photovoltaic applications. Notably, the PCE is only slightly changed by structural phase modification, suggesting that phase transitions induced by environmental conditions during device operation might not compromise device performance. △ Less

Submitted 18 June, 2025; originally announced June 2025.

Entangled Interlocked Diamond-like (Diamondiynes) Lattices

Authors: C. M. O. Bastos, E. J. A. dos Santos, R. A. F. Alves, Alexandre C. Dias, L. A. Ribeiro Junior, D. S. Galvão

Abstract: Diamondynes, a new class of diamond-like carbon allotropes composed of carbon with sp$^2$/sp$^3$-hybridized carbon networks, exhibit unique structural motifs that have not been previously reported in carbon materials. These architectures feature sublattices that are both interlocked and capable of relative movement. Using ab initio simulations, we have conducted an extensive investigation into the… ▽ More Diamondynes, a new class of diamond-like carbon allotropes composed of carbon with sp$^2$/sp$^3$-hybridized carbon networks, exhibit unique structural motifs that have not been previously reported in carbon materials. These architectures feature sublattices that are both interlocked and capable of relative movement. Using ab initio simulations, we have conducted an extensive investigation into the structural and electronic properties of five diamondyne structures. Our results show that diamondiynes are thermodynamically stable and exhibit wide electronic band gaps, from 2.2 eV to 4.0 eV. They are flexible yet highly resistant compared to other diamond-like structures. They have relatively small cohesive energy values, consistent with the fact that one diamondyne structure (2f-unsym) has already been experimentally realized. Our results provide new physical insights into diamond-like carbon networks and suggest promising directions for the development of porous, tunable frameworks with potential applications in energy storage and conversion. △ Less

Submitted 11 June, 2025; originally announced June 2025.

Comments: 6 pages

MSC Class: 00-XX ACM Class: I.2; J.6

First-Principles and Machine Learning Investigation of the Structural and Optoelectronic Properties of Dodecaphenylyne: A Novel Carbon Allotrope

Authors: Kleuton A. L. Lima, Jose A. S. Laranjeira, Nicolas F. Martins, Julio R. Sambrano, Alexandre C. Dias, Luiz A. Ribeiro Junior, Douglas S. Galvao

Abstract: We report the computational discovery and characterization of Dodecaphenylyne (DP), a novel carbon allotrope with a distinctive geometric arrangement. DP structural, thermodynamic, mechanical, electronic, and optical properties were evaluated using density functional theory and a machine learning interatomic potential trained explicitly for this material. The formation energy of -7.98 eV/atom indi… ▽ More We report the computational discovery and characterization of Dodecaphenylyne (DP), a novel carbon allotrope with a distinctive geometric arrangement. DP structural, thermodynamic, mechanical, electronic, and optical properties were evaluated using density functional theory and a machine learning interatomic potential trained explicitly for this material. The formation energy of -7.98 eV/atom indicates high thermodynamic stability, further supported by the absence of imaginary phonon modes and the preservation of structural integrity up to 1000 K in ab initio molecular dynamics simulations. Mechanical analysis reveals high in-plane stiffness with directional dependence: Young's modulus values of 469.09 GPa and 600.41 GPa along the x and y directions, respectively. Electronic band structure and projected density of states analyses confirm the DP semiconducting character. Calculations of carrier mobility using the deformation potential theory reveal pronounced anisotropy, with maximum values reaching up to $30.6 \times 10^4$ cm$^2$/V$\cdot$s (electrons, e) and $8.4 \times 10^4$ cm$^2$/V$\cdot$s (holes, h), much higher than the observed for other 2D materials. DP also exhibits anisotropic optical absorption in the visible and ultraviolet spectrum, highlighting its potential for optoelectronic applications. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Electronic and optical and topological properties of defects in bismuthene

Authors: Gabriel Elyas Gama Araujo, Andreia Luisa da Rosa, Alexandre Cavalheiro Dias, Thomas Frauenheim

Abstract: In this work we use first principles density-functional theory and Bethe-Salpeter equation together with tight-binding based maximally localized wannier functions (MLWF-TB) to investigate the electronic, optical and topological properties of two-dimensional bismuth (bismuthene) containing vacancy defects. We demonstrate that these properties depends on the shape and size of the nanopores. Furtherm… ▽ More In this work we use first principles density-functional theory and Bethe-Salpeter equation together with tight-binding based maximally localized wannier functions (MLWF-TB) to investigate the electronic, optical and topological properties of two-dimensional bismuth (bismuthene) containing vacancy defects. We demonstrate that these properties depends on the shape and size of the nanopores. Furthermore, \textit{ab initio} molecular dynamics (AIMD) simulations shows that all pores are thermally stable at room temperature. Finally, adsorption of gas phase small molecules indicates that these pores can serve as sensors, opening the path for further applications in gas separation and sensing. △ Less

Submitted 19 May, 2025; originally announced May 2025.

Optical properties of TiS$_3$ as a novel thin film for single-junction and tandem solar cells

Authors: Cesar E. P. Villegas, Enesio Marinho Jr, A. C. Dias, Pedro Venezuela, Alexandre R. Rocha

Abstract: Sub-micrometer thin films are promising platforms for emerging flexible photovoltaic devices. Although the current market already produces efficient solar cells, the average wafer thickness of these devices remains far from the sub-micrometer scale, making them susceptible to cracking under bending stress and thus precluding their use in flexible device applications. Due to its earth abundance, no… ▽ More Sub-micrometer thin films are promising platforms for emerging flexible photovoltaic devices. Although the current market already produces efficient solar cells, the average wafer thickness of these devices remains far from the sub-micrometer scale, making them susceptible to cracking under bending stress and thus precluding their use in flexible device applications. Due to its earth abundance, non-toxicity, and low elastic modulus, titanium trisulfide (TiS$_3$) has emerged as a promising alternative for flexible device applications. Here, using excited-state density functional calculations combined with the transfer matrix approach, we perform an optical analysis and assess the efficiency of a prototype photovoltaic device based on sub-micrometer TiS$_3$ thin films. Using optical constants obtained from our first-principles calculations, we evaluate the photovoltaic response of a single-junction device in the radiative limit, finding that a 140-nm-thick active layer achieves a maximum power conversion efficiency of approximately 22%. Additionally, we investigate tandem solar cells that incorporate TiS$_3$ into perovskite thin films, and find that the lower and upper power conversion efficiencies range from approximately 18% to 33%. Overall, our results suggest great potential for using TiS$_3$ thin films as an active layer in the design of highly efficient flexible solar cells. △ Less

Submitted 8 April, 2025; originally announced April 2025.

Electronic and optical properties of two-dimensional flat band triphosphides

Authors: Gabriel Elyas Gama Araujo, Lucca Moraes Gomes, Dominike Pacine de Andrade Deus, Alexandre Cavalheiro Dias, Andreia Luisa da Rosa

Abstract: In this work we use first-principles density-functional theory (DFT) calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasi-particle effects in 2D electronic and optical properties of triphosphide based two-dimensional materials XP$_3$ (X = Ga, Ge, As; In, Sn, Sb; Tl, Pb and… ▽ More In this work we use first-principles density-functional theory (DFT) calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasi-particle effects in 2D electronic and optical properties of triphosphide based two-dimensional materials XP$_3$ (X = Ga, Ge, As; In, Sn, Sb; Tl, Pb and Bi). We find that with exception of InP$_3$, all structures have indirect band gap. A noticeable feature is the appearance of flat valence bands associated to phosphorous atoms, mainly in InP$_3$ and GaP$_3$ structures. Furthermore, AIMD calculations show that 2D-XP$_3$ is stable at room temperature, with exception of TlP$_3$ monolayer, which shows a strong distortion yielding to a phase separation of the P and Tl layers. Finally, we show that monolayered XP$_3$ exhibits optical absorption with strong excitonic effects, thus revealing exciting features of these monolayered materials. △ Less

Submitted 4 April, 2025; originally announced April 2025.

Cracking Down on Fracture to Functionalise Damage

Authors: Leo de Waal, Matthaios Chouzouris, Marcelo A. Dias

Abstract: In this work we propose a novel relationship between topology and damage propagation in Maxwell lattices that redefines fracture as a functional design feature rather than mere degradation. We demonstrate that topologically protected modes, inherently robust against perturbations, localise along lattice discontinuities and govern the mechanical response. By precisely engineering the microstructure… ▽ More In this work we propose a novel relationship between topology and damage propagation in Maxwell lattices that redefines fracture as a functional design feature rather than mere degradation. We demonstrate that topologically protected modes, inherently robust against perturbations, localise along lattice discontinuities and govern the mechanical response. By precisely engineering the microstructure, we direct these modes to control stress distributions and trigger predictable, controlled damage. Our findings -- validated through comprehensive numerical simulations and experiments -- advance our understanding of nontrivial mechanical responses in Maxwell lattices and establish a clear framework for designing materials with improved fracture energy. This work paves the way for further exploration of topology-driven phenomena in mechanical systems and promises a new direction in the design of robust materials. △ Less

Submitted 28 March, 2025; originally announced March 2025.

Comments: arXiv admin note: text overlap with arXiv:2410.17100

Petal-Graphyne: A Novel 2D Carbon Allotrope for High-Performance Li and Na Ion Storage

Authors: Kleuton A. L. Lima, José A. S. Laranjeira, Nicolas F. Martins, Alexandre C. Dias, J ulio R. Sambrano, Douglas S. Galvão, Luiz A. Ribeiro Junior

Abstract: Using density functional theory simulations, this study introduces Petal-Graphyne (PLG), a novel multi-ring metallic structure composed of 4-, 8-, 10-, and 16-membered rings. Its structural, electronic, and lithium/sodium storage properties were comprehensively investigated. PLG exhibits a high theoretical capacity of 1004 mAh/g for Li, Na, and mixed Li/Na ions, surpassing conventional graphite an… ▽ More Using density functional theory simulations, this study introduces Petal-Graphyne (PLG), a novel multi-ring metallic structure composed of 4-, 8-, 10-, and 16-membered rings. Its structural, electronic, and lithium/sodium storage properties were comprehensively investigated. PLG exhibits a high theoretical capacity of 1004 mAh/g for Li, Na, and mixed Li/Na ions, surpassing conventional graphite anodes. The material remains metallic, with multiple band crossings at the Fermi level. The optimal energy barriers for Li (0.28 eV) and Na (0.25 eV) on PLG and favorable diffusion coefficients in both monolayer and multilayer configurations are unveiled. The open circuit voltages are 0.47 V for Li, 0.51 V for Na, and 0.54 V for mixed-ion storage, suggesting stable electrochemical performance. These results highlight PLG as a promising candidate for next-generation lithium and sodium-ion batteries, combining high storage capacity and efficient ion transport. △ Less

Submitted 27 March, 2025; originally announced March 2025.

Comments: 13 pages

MSC Class: 00-XX ACM Class: J.2; I.6

Physicochemical Characterization of a New 2D Semiconductor Carbon Allotrope, C16: An Investigation via Density Functional Theory and Machine Learning-based Molecular Dynamics

Authors: Kleuton A. L. Lima, Rodrigo A. F. Alves, Elie A. Moujaes, Alexandre C. Dias, Douglas S. Galvão, Marcelo L. Pereira Jr, Luiz A. Ribeiro Jr

Abstract: This study comprehensively characterizes, with suggested applications, a novel two-dimensional carbon allotrope, C$_{16}$, using Density Functional Theory and machine learning-based molecular dynamics. This nanomaterial is derived from naphthalene and bicyclopropylidene molecules, forming a planar configuration with sp$^2$ hybridization and featuring 3-, 4-, 6-, 8-, and 10-membered rings. Cohesive… ▽ More This study comprehensively characterizes, with suggested applications, a novel two-dimensional carbon allotrope, C$_{16}$, using Density Functional Theory and machine learning-based molecular dynamics. This nanomaterial is derived from naphthalene and bicyclopropylidene molecules, forming a planar configuration with sp$^2$ hybridization and featuring 3-, 4-, 6-, 8-, and 10-membered rings. Cohesive energy of \SI{-7.1}{\electronvolt/atom}, absence of imaginary frequencies in the phonon spectrum, and the retention of the system's topology after ab initio molecular dynamics simulations confirm the structural stability of C$_{16}$. The nanomaterial exhibits a semiconducting behavior with a direct band gap of \SI{0.59}{\electronvolt} and anisotropic optical absorption in the $y$ direction. Assuming a complete absorption of incident light, it registers a power conversion efficiency of \SI{13}{\percent}, demonstrating relatively good potential for applications in solar energy conversion. The thermoelectric figure of merit ($zT$) reaches 0.8 at elevated temperatures, indicating a reasonable ability to convert a temperature gradient into electrical power. Additionally, C$_{16}$ demonstrates high mechanical strength, with Young's modulus values of \SI{500}{\giga\pascal} and \SI{630}{\giga\pascal} in the $x$ and $y$ directions, respectively. Insights into the electronic, optical, thermoelectric, and mechanical properties of C$_{16}$ reveal its promising capability for energy conversion applications. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 22 pages

MSC Class: 00-XX ACM Class: J.2; I.6

Computational Characterization of the Recently Synthesized Pristine and Porous 12-Atom-Wide Armchair Graphene Nanoribbon

Authors: Djardiel da S. Gomes, Isaac M. Felix, Willian F. Radel, Alexandre C. Dias, Luiz A. Ribeiro Junior, Marcelo L. Pereira Junior

Abstract: Recently synthesized Porous 12-Atom-Wide Armchair Graphene Nanoribbons Nano Lett. 2024, 24, 10718-10723 exhibit tunable properties through periodic porosity, enabling precise control over their electronic, optical, thermal, and mechanical behavior. This work presents a comprehensive theoretical characterization of pristine and porous 12-AGNRs based on density functional theory (DFT) and molecular… ▽ More Recently synthesized Porous 12-Atom-Wide Armchair Graphene Nanoribbons Nano Lett. 2024, 24, 10718-10723 exhibit tunable properties through periodic porosity, enabling precise control over their electronic, optical, thermal, and mechanical behavior. This work presents a comprehensive theoretical characterization of pristine and porous 12-AGNRs based on density functional theory (DFT) and molecular dynamics (MD) simulations. DFT calculations reveal substantial electronic modifications, including band gap widening and the emergence of localized states. Analyzed within the Bethe-Salpeter equation (BSE) framework, optical properties highlight strong excitonic effects and significant absorption shifts. Thermal transport simulations indicate a pronounced reduction in conductivity due to enhanced phonon scattering at nanopores. At the same time, MD-based mechanical analysis shows decreased stiffness and strength while maintaining structural integrity. Despite these modifications, porous 12-AGNRs remain mechanically and thermally stable. These findings establish porosity engineering as a powerful strategy for tailoring graphene nanoribbons' functional properties, reinforcing their potential for nanoelectronic, optoelectronic, and thermal management applications. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: 11 pages and 5 figures

MSC Class: 00-xx ACM Class: J.2; I.6

Exploring Novel 2D Analogues of Goldene: Electronic, Mechanical, and Optical Properties of Silverene and Copperene

Authors: Emanuel J. A. dos Santos, Rodrigo A. F. Alves, Alexandre C. Dias, Marcelo L. Pereira Junior, Douglas S. Galvão, Luiz A. Ribeiro Junior

Abstract: Two-dimensional (2D) materials have garnered significant attention due to their unique properties and broad application potential. Building on the success of goldene, a monolayer lattice of gold atoms, we explore its proposed silver and copper analogs, silverene and copperene, using density functional theory calculations. Our findings reveal that silverene and copperene are energetically stable, w… ▽ More Two-dimensional (2D) materials have garnered significant attention due to their unique properties and broad application potential. Building on the success of goldene, a monolayer lattice of gold atoms, we explore its proposed silver and copper analogs, silverene and copperene, using density functional theory calculations. Our findings reveal that silverene and copperene are energetically stable, with formation energies of -2.3 eV/atom and -3.1 eV/atom, closely matching goldene's -2.9 eV/atom. Phonon dispersion and ab initio molecular dynamics simulations confirm their structural and dynamical stability at room temperature, showing no bond breaking or structural reconfiguration. Mechanical analyses indicate isotropy, with Young's moduli of 73 N/m, 44 N/m, and 59 N/m for goldene, silverene, and copperene, respectively, alongside Poisson's ratios of 0.46, 0.42, and 0.41. These results suggest comparable rigidity and deformation characteristics. Electronic band structure analysis highlights their metallic nature, with variations in the band profiles at negative energy levels. Despite their metallic character, these materials exhibit optical properties akin to semiconductors, pointing to potential applications in optoelectronics. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 24 pages and six figures

MSC Class: 00-xx ACM Class: J.2; I.6

A Microcanonical Inflection Point Analysis via Parametric Curves and its Relation to the Zeros of the Partition Function

Authors: Julio Cesar Siqueira Rocha, Rodrigo Alves Dias, Bismarck Vaz da Costa

Abstract: In statistical physics, phase transitions are arguably among the most extensively studied phenomena. In the computational approach to this field, the development of algorithms capable of estimating entropy across the entire energy spectrum in a single execution has highlighted the efficacy of microcanonical inflection point analysis, while Fisher's zeros technique has re-emerged as a powerful meth… ▽ More In statistical physics, phase transitions are arguably among the most extensively studied phenomena. In the computational approach to this field, the development of algorithms capable of estimating entropy across the entire energy spectrum in a single execution has highlighted the efficacy of microcanonical inflection point analysis, while Fisher's zeros technique has re-emerged as a powerful methodology for investigating these phenomena. This paper presents an alternative protocol for analyzing phase transitions using a parametrization of the entropy function in the microcanonical ensemble. We also provide a clear demonstration of the relation of the linear pattern of the Fisher's zeros on the complex inverse temperature map (a circle in the complex $x=e^{-β\varepsilon}$ map) with the order of the transition, showing that the latent heat is inversely related to the distance between the zeros. We study various model systems, including the Lennard-Jones cluster, the Ising, the XY, and the Zeeman models. By examining the behavior of thermodynamic quantities such as entropy and its derivatives in the microcanonical ensemble, we identify key features-such as loops and discontinuities in parametric curves-which signal phase transitions' presence and nature. This approach can facilitate the classification of phase transitions across various physical systems. △ Less

Submitted 5 July, 2025; v1 submitted 2 February, 2025; originally announced February 2025.

Comments: 13 pages, 10 figures

Architecting mechanisms of damage in topological metamaterials

Authors: Leo de Waal, Matthaios Chouzouris, Marcelo A. Dias

Abstract: Architecting mechanisms of damage in metamaterials by leveraging lattice topology and geometry poses a vital yet complex challenge, essential for engineering desirable mechanical responses. Of these metamaterials, Maxwell lattices, which are on the verge of mechanical stability, offer significant potential for advanced functionality. By leveraging their robust topological features, they enable pre… ▽ More Architecting mechanisms of damage in metamaterials by leveraging lattice topology and geometry poses a vital yet complex challenge, essential for engineering desirable mechanical responses. Of these metamaterials, Maxwell lattices, which are on the verge of mechanical stability, offer significant potential for advanced functionality. By leveraging their robust topological features, they enable precise control of effective elastic properties, manipulation of stress localisation and delocalisation across specific domains, and targeted global damage that follows local fracture events. In this work, we identify topology and geometry-dependent parameters that establish a simple, yet precise, framework for designing the behaviour of non-idealised Maxwell lattices and their damage processes. We numerically explore the underlying phenomenology to demonstrate how this framework can guide or arrest damage in lattices, both with and without domain walls and additional boundary constraints. Our approach uncovers a robust way to manipulate the mechanisms of damage and the path they follow in metamaterials, with further insight into crack arrest, diversion, and shielding. △ Less

Submitted 25 August, 2025; v1 submitted 22 October, 2024; originally announced October 2024.

Journal ref: Physical Review Research 7, 033177 2025

Raman Spectra and Excitonic Effects of the novel Ta$_2$Ni$_3$Te$_5$ Monolayer

Authors: Alexandre C. Dias, Raphael M. Tromer, Humberto R. Gutiérrez, Douglas S. Galvão, Elie A. Moujaes

Abstract: We have investigated the Raman spectrum and excitonic effects of the novel two-dimensional Ta$_2$Ni$_3$Te$_5$ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 eV and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could… ▽ More We have investigated the Raman spectrum and excitonic effects of the novel two-dimensional Ta$_2$Ni$_3$Te$_5$ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 eV and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify ten Raman and ten infrared active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and also presents a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the x-direction. △ Less

Submitted 24 September, 2024; originally announced September 2024.

Oscillating Magnetic Effect in BiFeO$_3$

Authors: Thiago Ferro, Adrielson Dias, Maria Clara, Luana Hildever, José Holanda

Abstract: The development of electric vehicles has led to a growing need for more efficient and environmentally friendly batteries. As a result, there is significant interest in researching new materials and techniques to enhance battery efficiency. One such material being explored is bismuth ferrite (BiFeO$_3$ or BFO), a perovskite with versatile properties. Researchers are particularly intrigued by the po… ▽ More The development of electric vehicles has led to a growing need for more efficient and environmentally friendly batteries. As a result, there is significant interest in researching new materials and techniques to enhance battery efficiency. One such material being explored is bismuth ferrite (BiFeO$_3$ or BFO), a perovskite with versatile properties. Researchers are particularly intrigued by the potential to control its antiferromagnetic magnetization using magnetic or electric fields. Here, a comprehensive analysis of BFO was conducted, with a focus on its behavior when subjected to oscillating magnetic fields. The research revealed that BFO is sensitive to the frequency and shape of these magnetic fields, leading to the discovery of a new effect related to the transmission of electromagnetic signals on its surface. This effect resulted in a significant increase in the power of the electromagnetic signal, representing a major technological breakthrough. According to the findings, this gain in power has not been observed in any system of this kind before. The study also demonstrated that BFO has the ability to detect magnetic fields through electrical output signals and vice versa, which is crucial for assessing the state and efficiency of batteries, thus contributing to significant advancements in energy storage technology. △ Less

Submitted 22 September, 2024; originally announced September 2024.

Inverse design of programmable shape-morphing kirigami structures

Authors: Xiaoyuan Ying, Dilum Fernando, Marcelo A. Dias

Abstract: Shape-morphing structures have the capability to transform from one state to another, making them highly valuable in engineering applications. In this study, it is propose a two-stage shape-morphing framework inspired by kirigami structures to design structures that can deploy from a compacted state to a prescribed state under certain mechanical stimuli -- although the framework may also be extend… ▽ More Shape-morphing structures have the capability to transform from one state to another, making them highly valuable in engineering applications. In this study, it is propose a two-stage shape-morphing framework inspired by kirigami structures to design structures that can deploy from a compacted state to a prescribed state under certain mechanical stimuli -- although the framework may also be extended to accommodate various physical fields, such as magnetic, thermal, and electric fields. The framework establishes a connection between the geometry and mechanics of kirigami structures. The proposed approach combines the finite element analysis (FEA), genetic algorithm (GA), and an analytical energy-based model to obtain kirigami designs with robustness and efficiency. △ Less

Submitted 15 June, 2024; originally announced June 2024.

On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer

Authors: Raphael M. Tromer, L. A. Ribeiro Júnior, Douglas S. Galvão, Alexandre C. Dias, Elie A. Moujaes

Abstract: Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetra… ▽ More Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination of squared and hexagonal rings in a buckled shape. Our findings reveal that tetragraphene is a semiconductor material with a direct electronic bandgap of 2.66 eV. Despite the direct nature of the electronic band structure, this material has an indirect exciton ground state of 2.30 eV, which results in an exciton binding energy of 0.36 eV. At ambient temperature, we obtain that the lattice thermal conductivity for tetragraphene is approximately 118 W/mK. Young's modulus and the shear modulus of tetragraphene are almost isotropic, with maximum values of 286.0 N/m and 133.7 N/m, respectively, while exhibiting a very low anisotropic Poisson ratio value of 0.09. △ Less

Submitted 30 January, 2024; originally announced January 2024.

Signature of excitonic insulators in phosphorene nanoribbons

Authors: A. F. P. de Oliveira, A. L. da Rosa, A. C. Dias

Abstract: Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention because of its unique anisotropic optical properties and quasi-one-dimensional (1D) excitons. We use first-principles calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasiparticle… ▽ More Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention because of its unique anisotropic optical properties and quasi-one-dimensional (1D) excitons. We use first-principles calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasiparticle effects of 2D and quasi-1D blue and black phosphorene nanoribbons. Our electronic structure calculations shows that both blue and black monolayered phases are semiconductors. On the other hand black phosphorene zigzag nanoribbons are metallic. Similar behavior is found for very thin blue phosphorene zig-zag and armchair nanoribbon. As a general behavior, the exciton binding energy decreases as the ribbon width increases, which highlights the importance of quantum confinement effects. The solution of the BSE shows that the blue phosphorene monolayer has an exciton binding energy four times higher than that of the black phosphorene counterpart. Furthermore, both monolayers show a different linear optical response with respect to light polarization, as black phosphorene is highly anisotropic. We find a similar, but less pronounced, optical anisotropy for blue phosphorene monolayer, caused exclusively by the quasi-particle effects. Finally, we show that some of the investigated nanoribbons show a spin-triplet excitonic insulator behavior, thus revealing exciting features of these nanoribbons and therefore provides important advances in the understanding of quasi-one dimensional phosphorus-based materials. △ Less

Submitted 7 January, 2024; originally announced January 2024.

Detecting magneto-optical interactions in nanostructures

Authors: Luana Hildever, Thiago Ferro, Adrielson Dias, André José, Francisco Estrada, José Holanda

Abstract: Effects due to magneto-optical interactions are responsible for most of the phenomena discovered in optoelectronics and spintronics. Magneto-optical interactions can generate elementary excitations of the order of light-magnetic matter, which can flow under certain conditions. Here, we observe the intensities of magneto-optical interactions in hexagonal arrays of magnetic nanowires using experimen… ▽ More Effects due to magneto-optical interactions are responsible for most of the phenomena discovered in optoelectronics and spintronics. Magneto-optical interactions can generate elementary excitations of the order of light-magnetic matter, which can flow under certain conditions. Here, we observe the intensities of magneto-optical interactions in hexagonal arrays of magnetic nanowires using experimental measurements and simulations. Nanowires of three materials (cobalt-Co, iron-Fe, and nickel-Ni) were electrodeposited on alumina membranes by the AC electrodeposition method. Our results reveal that the magneto-optical behavior can produce, under certain conditions, a kind of avalanche of magneto-optical interactions, which is dynamic. Such an observation shows the possibility of generating a magneto-optical current (spin-opto current). △ Less

Submitted 6 January, 2024; originally announced January 2024.

Three-state active lattice gas: a discrete Vicseklike model with excluded volume

Authors: Tiago Venzel Rosembach, Ana Luiza Novaes Dias, Ronald Dickman

Abstract: We study a discrete-space model of active matter with excluded volume. Particles are restricted to the sites of a triangular lattice, and can assume one of three orientations. Varying the density and noise intensity, Monte Carlo simulations reveal a variety of spatial patterns. Ordered states occur in the form of condensed structures, which (away from the full occupancy limit) coexist with a low-d… ▽ More We study a discrete-space model of active matter with excluded volume. Particles are restricted to the sites of a triangular lattice, and can assume one of three orientations. Varying the density and noise intensity, Monte Carlo simulations reveal a variety of spatial patterns. Ordered states occur in the form of condensed structures, which (away from the full occupancy limit) coexist with a low-density vapor. The condensed structures feature low particle mobility, particularly those that wrap the system via the periodic boundaries. As the noise intensity is increased, dense structures give way to a disordered phase. We characterize the parameter values associated with the condensed phases and perform a detailed study of the order-disorder transition at (1) full occupation and (2) at a density of 0.1. In the former case, the model possesses the same symmetry as the three-state Potts model and exhibits a continuous phase transition, as expected, with critical exponents consistent with those of the associated Potts model. In the low-density case, the transition is clearly discontinuous, with strong dependence of the final state upon the initial configuration, hysteresis,and nonmonotonic dependence of the Binder cumulant upon noise intensity. △ Less

Submitted 10 May, 2024; v1 submitted 14 December, 2023; originally announced December 2023.

Comments: 32 pages, 17 figures

Estimating the Number of States via the Rodeo Algorithm for Quantum Computation

Authors: Julio Cesar Siqueira Rocha, Raphael Fortes Infante Gomes, Wallon Anderson Tadaiesky Nogueira, Rodrigo Alves Dias

Abstract: In the realm of statistical physics, the number of states in which a system can be realized with a given energy is a key concept that bridges the microscopic and macroscopic descriptions of physical systems. For quantum systems, many approaches rely on the solution of the Schrödinger equation. In this work, we demonstrate how the recently developed rodeo algorithm can be utilized to determine the… ▽ More In the realm of statistical physics, the number of states in which a system can be realized with a given energy is a key concept that bridges the microscopic and macroscopic descriptions of physical systems. For quantum systems, many approaches rely on the solution of the Schrödinger equation. In this work, we demonstrate how the recently developed rodeo algorithm can be utilized to determine the number of states associated with all energy levels without any prior knowledge of the eigenstates. Quantum computers, with their innate ability to address the intricacies of quantum systems, make this approach particularly promising for the study of the thermodynamics of those systems. To illustrate the procedure's effectiveness, we apply it to compute the number of states of the 1D transverse-field Ising model and, consequently, its specific heat, proving the reliability of the method presented here. △ Less

Submitted 26 September, 2024; v1 submitted 7 December, 2023; originally announced December 2023.

Comments: 6 pages, 4 figures

On Micropolar Elastic Foundations

Authors: Adrianos E. F. Athanasiadis, Michal K. Budzik, Dilum Fernando, Marcelo A. Dias

Abstract: The modelling of heterogeneous and architected materials poses a significant challenge, demanding advanced homogenisation techniques. However, the complexity of this task can be considerably simplified through the application of micropolar elasticity. Conversely, elastic foundation theory is widely employed in fracture mechanics and the analysis of delamination propagation in composite materials.… ▽ More The modelling of heterogeneous and architected materials poses a significant challenge, demanding advanced homogenisation techniques. However, the complexity of this task can be considerably simplified through the application of micropolar elasticity. Conversely, elastic foundation theory is widely employed in fracture mechanics and the analysis of delamination propagation in composite materials. This study aims to amalgamate these two frameworks, enhancing the elastic foundation theory to accommodate materials exhibiting micropolar behaviour. Specifically, we present a novel theory of elastic foundation for micropolar materials, employing stress potentials formulation and a unique normalisation approach. Closed-form solutions are derived for stress and couple stress reactions inherent in such materials, along with the associated restoring stiffness. The validity of the proposed theory is established through verification using the double cantilever beam configuration. Concluding our study, we elucidate the benefits and limitations of the developed theory by quantifying the derived parameters for materials known to exhibit micropolar behaviour. This integration of micropolar elasticity into the elastic foundation theory not only enhances our understanding of material responses but also provides a versatile framework for the analysis of heterogeneous materials in various engineering applications. △ Less

Submitted 24 February, 2024; v1 submitted 2 November, 2023; originally announced November 2023.

Journal ref: European Journal of Mechanics - A/Solids, 105, 105277, 2024

Toughening mechanisms and damage propagation in Architected-Interfaces

Authors: Michelle L. S. Hedvard, Marcelo A. Dias, Michal K. Budzik

Abstract: We investigate fracture toughness of architected interfaces and their ability to maintain structural integrity and provide stable damage propagation conditions beyond the failure load. We propose theoretical and numerical frameworks to evaluate the fracture properties of architected interfaces sandwiched between two (face) materials. The microscopic geometries of these interfaces are chosen as 2D… ▽ More We investigate fracture toughness of architected interfaces and their ability to maintain structural integrity and provide stable damage propagation conditions beyond the failure load. We propose theoretical and numerical frameworks to evaluate the fracture properties of architected interfaces sandwiched between two (face) materials. The microscopic geometries of these interfaces are chosen as 2D cells--pillar, tetrahedron, and hexagon--as well as their 3D counterparts--namely, pillar array, octet truss, and Kelvin cell. Our model, both numerical and analytical, exhibits a high level of accuracy in predicting the compliance before failure and failure loads. Novel results are obtained during the damage propagation regime, indicating fulfilment of the so-called fail-safe design. Some of the cell geometries unfold during fracture, thus increasing the failure load and ensuring stable and controlled damage propagation conditions. △ Less

Submitted 24 February, 2024; v1 submitted 1 May, 2023; originally announced May 2023.

Journal ref: International Journal of Solids and Structures, 288, 112600, 2024

An experimental analysis from the magnetic interactions in nanowire arrays

Authors: Wibson W. G. Silva, Adrielson de A. Dias, Alexandre R. Rodrigues, Francisco E. Chávez, Rafael A. de Oliveira, José Holanda

Abstract: We study the magnetic interactions experimentally in nanostructures of nanowire arrays. The intensity value obtained from the interactions provides information about its magnetic behavior. We observed two types of experimental magnetic behavior, i. e., demagnetized and magnetized. Our approach represents the first experimental way to analyze the magnetic behavior of a nanostructure considering its… ▽ More We study the magnetic interactions experimentally in nanostructures of nanowire arrays. The intensity value obtained from the interactions provides information about its magnetic behavior. We observed two types of experimental magnetic behavior, i. e., demagnetized and magnetized. Our approach represents the first experimental way to analyze the magnetic behavior of a nanostructure considering its magnetic dependence, which is very important for applications in sensors, for example. △ Less

Submitted 23 October, 2022; originally announced October 2022.

A High Throughput Study of both Compositionally Graded and Homogeneous Fe-Pt Thin Films

Authors: Yuan Hong, Isabelle de Moraes, Gabriel Gomez Eslava, Stephane Grenier, Edith Bellet-Amalric, Andre Dias, Marlio Bonfim, Laurent Ranno, Thibaut Devillers, Nora M. Dempsey

Abstract: Compositionally graded Fe-Pt thin films were prepared on stationary 100 mm Si substrates by magnetron sputtering a base target of Fe on which a piece of Pt is asymmetrically positioned. Energy Dispersive X-Ray analysis was used to map the variation in film composition across the substrate, as a function of the size of the Pt piece. A scanning polar Magneto-Optical-Kerr-Effect system was used to pr… ▽ More Compositionally graded Fe-Pt thin films were prepared on stationary 100 mm Si substrates by magnetron sputtering a base target of Fe on which a piece of Pt is asymmetrically positioned. Energy Dispersive X-Ray analysis was used to map the variation in film composition across the substrate, as a function of the size of the Pt piece. A scanning polar Magneto-Optical-Kerr-Effect system was used to probe the influence of composition and post-deposition annealing conditions (temperature and time) on coercivity. In this way the maximum coercivity achievable for the sputtering system used could be established in a high throughput fashion. The evolution in coercivity with composition was correlated with the formation of L10 FePt and changes in its lattice parameters, as determined by scanning X-ray diffraction. High throughput coercivity mapping was then carried out on homogeneous Fe-Pt thin films of different composition treated to different annealing conditions. This study serves as a step towards the integration of coercive FePt films into collectively fabricated devices. △ Less

Submitted 30 October, 2021; originally announced November 2021.

On local kirigami mechanics II: Stretchable creased solutions

Authors: Souhayl Sadik, Martin G. Walker, Marcelo A. Dias

Abstract: Following on Part I of this work series on local kirigami mechanics, we present a study of a discretely creased mechanism as a model to investigate the mechanics of the basic geometric building block of kirigami--the e-cone. We consider an annular disk with a single radial slit discritised by a series of radial creases connecting kinematically flat rigid panels. The creases allow both relative rot… ▽ More Following on Part I of this work series on local kirigami mechanics, we present a study of a discretely creased mechanism as a model to investigate the mechanics of the basic geometric building block of kirigami--the e-cone. We consider an annular disk with a single radial slit discritised by a series of radial creases connecting kinematically flat rigid panels. The creases allow both relative rotation and separation between panels, capturing both bending and stretching deformations. Admissible equilibrium configurations are obtained by penalising these deformations using elastic springs with stiffnesses derived from compatible continuum plate deformations. This provides a tool to study both inextensible and extensible e-cone configurations due to opening of the slit and rotation of its lips. This creased model hence offers the possibility to study the e-cone away from its isometric limit, i.e., for plates with finite thickness, and explore the full range of post-buckling (far-from-threshold) behaviour as well as initial buckling (near-threshold) instability. Our local approach provides a fundamental understanding of kirigami phenomenology, underpinned by a proper theoretical approach to geometry and mechanics. △ Less

Submitted 7 September, 2021; originally announced September 2021.

Re-entrant tensegrity: A three-periodic, chiral, tensegrity structure that is auxetic

Authors: Mathias Oster, Marcelo A. Dias, Timo de Wolff, Myfanwy E. Evans

Abstract: We present a three-periodic, chiral, tensegrity structure and demonstrate that it is auxetic. Our tensegrity structure is constructed using the chiral symmetry Π+ cylinder packing, transforming the cylinders themselves to the elastic elements and cylinder contacts to incompressible rods. The resulting structure displays local re-entrant geometry at its vertices, and is shown to be auxetic when mod… ▽ More We present a three-periodic, chiral, tensegrity structure and demonstrate that it is auxetic. Our tensegrity structure is constructed using the chiral symmetry Π+ cylinder packing, transforming the cylinders themselves to the elastic elements and cylinder contacts to incompressible rods. The resulting structure displays local re-entrant geometry at its vertices, and is shown to be auxetic when modelled as an equilibrium configuration of spatial constraints subject to a quasi-static deformation. When the tensegrity structure is subsequently modelled as a lattice material with elastic elements, the auxetic behaviour is again confirmed through finite element modelling as well as demonstrated with a 3d printed example. The cubic symmetry of the structure means that the behaviour is independent of the chosen stretching direction and the auxetic behaviour is observed in both perpendicular directions. This structure could be the simplest three-dimensional analogue to the two-dimensional re-entrant honeycomb. This, alongside the chirality of the structure, make it an interesting design target for multifunctional materials. △ Less

Submitted 10 May, 2021; originally announced May 2021.

Can confined mechanical metamaterials replace adhesives?

Authors: Adrianos E. F. Athanasiadis, Marcelo A. Dias, Michal K. Budzik

Abstract: The subject of mechanical metamaterials has been gaining significant attention, however, their widespread application is still halted. Such materials are usually considered as stand-alone, vis-à-vis all characteristic length scales being associated solely with geometry of material itself. In this work we propose novel application of mechanical metamaterials as interface regions joining two materia… ▽ More The subject of mechanical metamaterials has been gaining significant attention, however, their widespread application is still halted. Such materials are usually considered as stand-alone, vis-à-vis all characteristic length scales being associated solely with geometry of material itself. In this work we propose novel application of mechanical metamaterials as interface regions joining two materials with potential of replacing bulk adhesives. This idea leads into paradigm shifts for both metamaterials and adhesive joints. In specific, we outline methodology for testing and evaluating confined lattice materials within fracture mechanics framework. The theoretical and numerical approaches are inter-winded, revealing a set of critical parameters that needs to be considered during design process. Lattices that are stretching and bending dominated are explored and failure maps are proposed, indicating susceptibility to a certain failure mode depending on level of confinement and characteristic dimension of each lattice's unit cells. △ Less

Submitted 16 August, 2021; v1 submitted 6 April, 2021; originally announced April 2021.

Magnon-polaron formation in XXZ quantum Heisenberg chains

Authors: D. Morais, F. A. B. F. de Moura W. S. Dias

Abstract: We study the formation of magnon-polaron excitations and the consequences of different time scales between the magnon and lattice dynamics. The spin-spin interactions along the 1D lattice are ruled by a Heisenberg Hamiltonian in the anisotropic form XXZ, in which each spin exhibits a vibrational degree of freedom around its equilibrium position. By considering a magnetoelastic coupling as a linear… ▽ More We study the formation of magnon-polaron excitations and the consequences of different time scales between the magnon and lattice dynamics. The spin-spin interactions along the 1D lattice are ruled by a Heisenberg Hamiltonian in the anisotropic form XXZ, in which each spin exhibits a vibrational degree of freedom around its equilibrium position. By considering a magnetoelastic coupling as a linear function of the relative displacement between nearest-neighbor spins, results provide an original framework for achieving a hybridized state of magnon-polaron. Such state is characterized by high cooperation between the underlying excitations, where the traveling or stationary formation of magnon-polaron depends on the effective magnetoelastic coupling. A systematic investigation reveals the critical amount of the magnon-lattice interaction ($χ_c$) necessary to emergence of the stationary magnon-polaron quasi-particle. Different characteristic time scales of the magnon and the vibrational dynamics unveiled the threshold between the two regimes, as well as a limiting value of critical magnetoelastic interaction, above which the magnon velocity no longer interferes at the critical magnetoelastic coupling capable of inducing the stationary regime. △ Less

Submitted 3 January, 2021; originally announced January 2021.

Comments: 8 pages, 10 figures

Journal ref: Phys. Rev. B 103, 195445 (2021)

On Local Kirigami Mechanics I: Isometric Conical Solutions

Authors: Souhayl Sadik, Marcelo A. Dias

Abstract: Over the past decade, kirigami--the Japanese art of paper cutting--has been playing an increasing role in the emerging field of mechanical metamaterials and a myriad of other mechanical applications. Nonetheless, a deep understanding of the mathematics and mechanics of kirigami structures is yet to be achieved in order to unlock their full potential to pioneer more advanced applications in the fie… ▽ More Over the past decade, kirigami--the Japanese art of paper cutting--has been playing an increasing role in the emerging field of mechanical metamaterials and a myriad of other mechanical applications. Nonetheless, a deep understanding of the mathematics and mechanics of kirigami structures is yet to be achieved in order to unlock their full potential to pioneer more advanced applications in the field. In this work, we study the most fundamental geometric building block of kirigami: a thin sheet with a single cut. We consider a reduced two-dimensional plate model of a circular thin disk with a radial slit and investigate its deformation following the opening of the slit and the rotation of its lips. In the isometric limit--as the thickness of the disk approaches zero--the elastic energy has no stretching contribution and the thin sheet takes a conical shape known as the e-cone. We solve the post-buckling problem for the e-cone in the geometrically nonlinear setting assuming a Saint Venant-Kirchhoff constitutive plate model; we find closed-form expressions for the stress fields and show the geometry of the e-cone to be governed by the spherical elastica problem. This allows us to fully map out the space of solutions and investigate the stability of the post-buckled e-cone problem assuming mirror symmetric boundary conditions on the rotation of the lips on the open slit. △ Less

Submitted 27 February, 2021; v1 submitted 7 September, 2020; originally announced September 2020.

Cutting holes in bistable folds

Authors: T. Yu, I. Andrade-Silva, M. A. Dias, J. A. Hanna

Abstract: A folded disk is bistable, as it can be popped through to an inverted state with elastic energy localized in a small, highly-deformed region on the fold. Cutting out this singularity relaxes the surrounding material and leads to a loss of bistability when the hole dimensions reach a critical size. These dimensions are strongly anisotropic and feature a surprising re-entrant behavior, such that rem… ▽ More A folded disk is bistable, as it can be popped through to an inverted state with elastic energy localized in a small, highly-deformed region on the fold. Cutting out this singularity relaxes the surrounding material and leads to a loss of bistability when the hole dimensions reach a critical size. These dimensions are strongly anisotropic and feature a surprising re-entrant behavior, such that removal of additional material can re-stabilize the inverted state. A model of the surface as a wide annular developable strip is found to capture the qualitative observations in experiments and simulations. These phenomena are consequential to the mechanics and design of crumpled elastic sheets, developable surfaces, origami and kirigami, and other deployable and compliant structures. △ Less

Submitted 24 May, 2021; v1 submitted 27 August, 2020; originally announced August 2020.

Comments: whither the singularity?

Tunable wrinkling of thin nematic liquid crystal elastomer sheets

Authors: Madison S. Krieger, Marcelo A. Dias

Abstract: Instabilities in thin elastic sheets, such as wrinkles, are of broad interest both from a fundamental viewpoint and also because of their potential for engineering applications. Nematic liquid crystal elastomers offer a new form of control of these instabilities through direct coupling between microscopic degrees of freedom, resulting from orientational ordering of rod-like molecules, and macrosco… ▽ More Instabilities in thin elastic sheets, such as wrinkles, are of broad interest both from a fundamental viewpoint and also because of their potential for engineering applications. Nematic liquid crystal elastomers offer a new form of control of these instabilities through direct coupling between microscopic degrees of freedom, resulting from orientational ordering of rod-like molecules, and macroscopic strain. By a standard method of dimensional reduction, we construct a plate theory for thin sheets of nematic elastomer. We then apply this theory to the study of the formation of wrinkles due to compression of a thin sheet of nematic liquid crystal elastomer atop an elastic or fluid substrate. We find the scaling of the wrinkle wavelength in terms of material parameters and the applied compression. The wavelength of the wrinkles is found to be non-monotonic in the compressive strain owing to the presence of the nematic. Finally, due to soft modes, the critical stress for the appearance of wrinkles can be much higher than in an isotropic elastomer and depends nontrivially on the manner in which the elastomer was prepared. △ Less

Submitted 24 June, 2019; originally announced June 2019.

Journal ref: Phys. Rev. E 100, 022701 (2019)

Foldable Cones as a Framework for Nonrigid Origami

Authors: I. Andrade, M. Adda-Bedia, M. A. Dias

Abstract: The study of origami-based mechanical metamaterials usually focuses on the kinematics of deployable structures made of an assembly of rigid flat plates connected by hinges. When the elastic response of each panel is taken into account, novel behaviors take place, as in the case of foldable cones (f-cones): circular sheets decorated by radial creases around which they can fold. These structures exh… ▽ More The study of origami-based mechanical metamaterials usually focuses on the kinematics of deployable structures made of an assembly of rigid flat plates connected by hinges. When the elastic response of each panel is taken into account, novel behaviors take place, as in the case of foldable cones (f-cones): circular sheets decorated by radial creases around which they can fold. These structures exhibit bistability, in the sense that they can snap-through from one metastable configuration to another. In this work, we study the elastic behavior of isometric f-cones for any deflection and crease mechanics, which introduce nonlinear corrections to a linear model studied previously. Furthermore, we test the inextensibility hypothesis by means of a continuous numerical model that includes both the extended nature of the creases, stretching and bending deformations of the panels. The results show that this phase field-like model could become an efficient numerical tool for the study of realistic origami structures. △ Less

Submitted 6 June, 2019; originally announced June 2019.

Journal ref: Phys. Rev. E 100, 033003 (2019)

Overcurvature induced multistability of linked conical frusta: How a `bendy straw' holds its shape

Authors: Nakul P. Bende, Tian Yu, Nicholas A. Corbin, Marcelo A. Dias, Christian D. Santangelo, James A. Hanna, Ryan C. Hayward

Abstract: We study the origins of multiple mechanically stable states exhibited by an elastic shell comprising multiple conical frusta, a geometry common to reconfigurable corrugated structures such as `bendy straws'. This multistability is characterized by mechanical stability of axially extended and collapsed states, as well as a partially inverted `bent' state that exhibits stability in any azimuthal dir… ▽ More We study the origins of multiple mechanically stable states exhibited by an elastic shell comprising multiple conical frusta, a geometry common to reconfigurable corrugated structures such as `bendy straws'. This multistability is characterized by mechanical stability of axially extended and collapsed states, as well as a partially inverted `bent' state that exhibits stability in any azimuthal direction. To understand the origin of this behavior, we study how geometry and internal stress affect the stability of linked conical frusta. We find that tuning geometrical parameters such as the frustum heights and cone angles can provide axial bistability, whereas stability in the bent state requires a sufficient amount of internal pre-stress, resulting from a mismatch between the natural and geometric curvatures of the shell. We analyze the latter effect through curvature analysis during deformation using X-ray computed tomography (CT), and with a simple mechanical model that captures the qualitative behavior of these highly reconfigurable systems. △ Less

Submitted 7 August, 2018; originally announced August 2018.

Comments: Total: 12 pages; Main text: 7 figures; Supporting info: Text, 6 figures, 4 movies

Multistable Kirigami for Tunable Architected Materials

Authors: Yi Yang, Marcelo A. Dias, Douglas P. Holmes

Abstract: In nature, materials such as ferroelastics and multiferroics can switch their microstructure in response to external stimuli, and this reconfiguration causes a simultaneous modulation of its material properties. Rapid prototyping technologies have enabled origami and kirigami-inspired architected materials to provide a means for designing shape-shifting structures, and here we show how multistable… ▽ More In nature, materials such as ferroelastics and multiferroics can switch their microstructure in response to external stimuli, and this reconfiguration causes a simultaneous modulation of its material properties. Rapid prototyping technologies have enabled origami and kirigami-inspired architected materials to provide a means for designing shape-shifting structures, and here we show how multistable structures inspired by kirigami provide novel design criteria for preparing mechanical metamaterials with tunable properties. By changing the geometry of kirigami unit cells, we obtain multistable kirigami lattice structures endowed with a bistable snap-through mechanism. We demonstrate the precise control of material stiffness, along with the ability to tune this property in situ by locally and reversibly switching the unit cell configurations. We anticipate these mechanical metamaterials will provide a platform to achieve in situ tunable electrical, optical, and mechanical properties for a variety of applications in multifunctional materials, two-dimensional materials, and soft robotics. △ Less

Submitted 20 November, 2018; v1 submitted 17 July, 2018; originally announced July 2018.

Journal ref: Phys. Rev. Materials 2, 110601 (2018)