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Physically motivated iso-orbital indicator for meta-GGA exchange functionals
Authors:
Jeet Sharma,
Abhishek Bhattacharjee,
Bikash Patra,
Prasanjit Samal
Abstract:
The iso-orbital indicator $α= (τ- τ^\mathrm{vW})/τ^\mathrm{UEG}$ is a key ingredient of meta-generalized gradient approximation (meta-GGA) functionals, but diverges in low-density tails , causing unphysical exchange potentials and systematic band gap errors as noted in [J. Chem. Phys. 150, 161101 (2019)]. We replace the denominator of $α$ with a physically motivated Pauli KED drawn from the orbita…
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The iso-orbital indicator $α= (τ- τ^\mathrm{vW})/τ^\mathrm{UEG}$ is a key ingredient of meta-generalized gradient approximation (meta-GGA) functionals, but diverges in low-density tails , causing unphysical exchange potentials and systematic band gap errors as noted in [J. Chem. Phys. 150, 161101 (2019)]. We replace the denominator of $α$ with a physically motivated Pauli KED drawn from the orbital-free DFT literature, eliminating the divergence in the low density atomic tail without any empirical regularization parameter. Testing two such enhancement factors: LKT and PGS, within the r$^2$SCAN and MS2 exchange functionals, we find that the modified indicators suppress spurious oscillations in the semilocal exchange potential and restore correct electron localization in atomic tails. For a ten-member cubic semiconductor benchmark, the band gap mean absolute error is reduced by 41.1 % for r$^2$SCAN@PGS and 48.8 % for MS2@PGS, while cohesive energy accuracy is largely preserved. The consistent improvement across two functionals with distinct constructions confirms a physical rather than functional specific origin, and motivates further development of meta-GGA functionals with constraint satisfying iso-orbital indicators.
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Submitted 20 July, 2026;
originally announced July 2026.
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Beyond lead halide perovskites: visible light photovoltaics with phase engineered bismuth-based oxide double-perovskites, Bi2MCrO6 (M = Fe, Mn)
Authors:
N P Vikas,
Ranjit K Pradhan,
Somdutta Mukherjee,
Udai P Singh,
Biplab K Patra,
Ravi P Srivastava,
Amritendu Roy
Abstract:
Lead poisoning and notorious ambient instability in lead-based halide perovskites pave the way for the exploration of alternative materials for affordable and efficient solar cell fabrication. An important prerequisite to this end is the optoelectronic evaluation of the proposed material. Here we report, optoelectronic characterization of Bi2FeCrO6 (BFCO) and Bi2MnCrO6 (BMCO) thin films vis-à-vis…
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Lead poisoning and notorious ambient instability in lead-based halide perovskites pave the way for the exploration of alternative materials for affordable and efficient solar cell fabrication. An important prerequisite to this end is the optoelectronic evaluation of the proposed material. Here we report, optoelectronic characterization of Bi2FeCrO6 (BFCO) and Bi2MnCrO6 (BMCO) thin films vis-à-vis performance of photovoltaic cells. Solution-deposited thin films (350-450 nm) of the above compositions demonstrate a double-perovskite structure with monoclinic P21/c symmetry, albeit with mixed cation valences and deep-level defects. A thorough optoelectronic evaluation exhibits large optical absorption in the visible range (α ~ 104 -105 cm-1), and high carrier density, ~1017-20 cm-3. Ultraviolet photoelectron spectroscopy measurement allowed determination of the positions of the band-edges (valence band maximum and conduction band minimum), required for the selection of carrier transport layers. In its first, BMCO-based FTO/SnO2/BMCO/Spiro-OMeTAD/Ag solar cell produced a maximum 3.56% conversion efficiency. Using numerical simulation, we predict that with suitable defect control, the above conversion efficiency can increase significantly.
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Submitted 5 May, 2026;
originally announced May 2026.
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Evidence of electronic instability driven structural distortion in the nodal line semimetal CoSn$_2$
Authors:
Suman Nandi,
Bishal Maity,
Shovan Dan,
Khadiza Ali,
Bikash Patra,
Anshuman Mondal,
Gaston Garbarino,
Pierre Rodière,
Sitaram Ramakrishnan,
Bahadur Singh,
Arumugam Thamizhavel
Abstract:
Understanding the mechanisms that drive spontaneous rotational symmetry breaking in correlated electron systems is a central challenge in condensed matter physics. Although such symmetry breaking phases have been studied in low-dimensional and strongly correlated materials, its emergence in structurally simpler compounds remains less explored. Here, we investigate non-magnetic CoSn$_2$ that is a c…
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Understanding the mechanisms that drive spontaneous rotational symmetry breaking in correlated electron systems is a central challenge in condensed matter physics. Although such symmetry breaking phases have been studied in low-dimensional and strongly correlated materials, its emergence in structurally simpler compounds remains less explored. Here, we investigate non-magnetic CoSn$_2$ that is a centrosymmetric intermetallic compound crystallizing in a tetragonal structure at ambient conditions, and discover an electronically driven symmetry breaking instability. Electrical resistivity reveals a distinct change in the slope below 25 K, deviating from the expected Bloch-Grüneisen behavior. This anomaly is attributed towards a structural change as at 22 K single crystal X-ray diffraction using synchrotron radiation uncovers weak superlattice reflections that leads to a doubling of $\textbf{a}$ and $\textbf{c}$, resulting in a 4-fold superstructure. The symmetry of the lattice reduces from tetragonal to acentric monoclinic but without any discernible monoclinic distortion down to 10 K. This structural transition is accompanied by a twofold symmetry in angular magnetoresistance, contrasting the fourfold symmetry observed at higher temperatures. First-principles calculations show no phonon softening but reveal enhanced electronic susceptibility, suggesting an electronic instability. Polarization-dependent ARPES measurements further identify a strong orbital anisotropy dominated by the in-plane Co-$d_{xy}$ states. Collectively, our results point to an electronic instability driven structural distortion in CoSn$_2$, offering a rare platform to study symmetry breaking in a non-magnetic metallic system.
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Submitted 27 September, 2025;
originally announced September 2025.
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Operating two exchange-only qubits in parallel
Authors:
Mateusz T. Mądzik,
Florian Luthi,
Gian Giacomo Guerreschi,
Fahd A. Mohiyaddin,
Felix Borjans,
Jason D. Chadwick,
Matthew J. Curry,
Joshua Ziegler,
Sarah Atanasov,
Peter L. Bavdaz,
Elliot J. Connors,
J. Corrigan,
H. Ekmel Ercan,
Robert Flory,
Hubert C. George,
Benjamin Harpt,
Eric Henry,
Mohammad M. Islam,
Nader Khammassi,
Daniel Keith,
Lester F. Lampert,
Todor M. Mladenov,
Randy W. Morris,
Aditi Nethwewala,
Samuel Neyens
, et al. (16 additional authors not shown)
Abstract:
Semiconductors are among the most promising platforms to implement large-scale quantum computers, as advanced manufacturing techniques allow fabrication of large quantum dot arrays. Various qubit encodings can be used to store and manipulate quantum information on these quantum dot arrays. Regardless of qubit encoding, precise control over the exchange interaction between electrons confined in qua…
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Semiconductors are among the most promising platforms to implement large-scale quantum computers, as advanced manufacturing techniques allow fabrication of large quantum dot arrays. Various qubit encodings can be used to store and manipulate quantum information on these quantum dot arrays. Regardless of qubit encoding, precise control over the exchange interaction between electrons confined in quantum dots in the array is critical. Furthermore, it is necessary to execute high-fidelity quantum operations concurrently to make full use of the limited coherence of individual qubits. Here, we demonstrate the parallel operation of two exchange-only qubits, consisting of six quantum dots in a linear arrangement. Using randomized benchmarking techniques, we show that issuing pulses on the five barrier gates to modulate exchange interactions in a maximally parallel way maintains the quality of qubit control relative to sequential operation. The techniques developed to perform parallel exchange pulses can be readily adapted to other quantum-dot based encodings. Moreover, we show the first experimental demonstrations of an iSWAP gate and of a charge-locking Pauli spin blockade readout method. The results are validated using cross-entropy benchmarking, a technique useful for performance characterization of larger quantum computing systems; here it is used for the first time on a quantum system based on semiconductor technology.
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Submitted 3 October, 2025; v1 submitted 1 April, 2025;
originally announced April 2025.
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Imprinting electrically switchable scalar spin chirality by anisotropic strain in a Kagome antiferromagnet
Authors:
Debjoty Paul,
Shivesh Yadav,
Shikhar Gupta,
Bikash Patra,
Nilesh Kulkarni,
Debashis Mondal,
Kaushal Gavankar,
Sourav K. Sahu,
Biswarup Satpati,
Bahadur Singh,
Owen Benton,
Shouvik Chatterjee
Abstract:
Topological chiral antiferromagnets, such as Mn$_{3}$Sn, are emerging as promising materials for next-generation spintronic devices due to their intrinsic transport properties linked to exotic magnetic configurations. Here, we demonstrate that anisotropic strain in Mn$_{3}$Sn thin films offers a novel approach to manipulate the magnetic ground state, unlocking new functionalities in this material.…
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Topological chiral antiferromagnets, such as Mn$_{3}$Sn, are emerging as promising materials for next-generation spintronic devices due to their intrinsic transport properties linked to exotic magnetic configurations. Here, we demonstrate that anisotropic strain in Mn$_{3}$Sn thin films offers a novel approach to manipulate the magnetic ground state, unlocking new functionalities in this material. Anisotropic strain reduces the point group symmetry of the manganese (Mn) Kagome triangles from $C_{3v}$ to $C_{1}$, significantly altering the energy landscape of the magnetic states in Mn$_{3}$Sn. This symmetry reduction enables even a tiny in-plane Dzyaloshinskii-Moriya (DM) interaction to induce canting of the Mn spins out of the Kagome plane. The modified magnetic ground state introduces a finite scalar spin chirality and results in a significant Berry phase in momentum space. Consequently, a large anomalous Hall effect emerges in the Kagome plane at room temperature - an effect that is absent in the bulk material. Moreover, this two-fold degenerate magnetic state enables the creation of multiple-stable, non-volatile anomalous Hall resistance (AHR) memory states. These states are field-stable and can be controlled by thermal assisted current-induced magnetization switching requiring modest current densities and small bias fields, thereby offering a compelling new functionality in Mn$_{3}$Sn for spintronic applications.
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Submitted 8 June, 2025; v1 submitted 4 November, 2024;
originally announced November 2024.
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High-order van Hove singularities and nematic instability in the kagome superconductor CsTi$_3$Bi$_5$
Authors:
Bikash Patra,
Amrita Mukherjee,
Bahadur Singh
Abstract:
ATi$_3$Bi$_5$ (A = Cs or Rb) are emerging topological kagome metals that exhibit superconductivity and nematicity without intertwining translational symmetry-breaking charge orders. In this work, we explore the fermiology of their titanium kagome electrons and identify a set of sublattice-pure, high-order van Hove singularities (VHSs) that can suppress charge ordering and enhance electronic correl…
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ATi$_3$Bi$_5$ (A = Cs or Rb) are emerging topological kagome metals that exhibit superconductivity and nematicity without intertwining translational symmetry-breaking charge orders. In this work, we explore the fermiology of their titanium kagome electrons and identify a set of sublattice-pure, high-order van Hove singularities (VHSs) that can suppress charge ordering and enhance electronic correlations and superconductivity. Our calculations of charge susceptibility for kagome bands with both normal and high-order VHSs emphasize the role of these VHSs in driving electronic nematicity in CsTi$_3$Bi$_5$. Additionally, we compute the phonon spectrum and electron-phonon interactions for CsTi$_3$Bi$_5$ under pristine, doped, and kagome-exposed surface conditions, revealing its robustness against structural instabilities while enhancing the superconducting transition temperature. Our work positions ATi$_3$Bi$_5$ as a key platform for investigating superconductivity and electronic nematicity without translational symmetry-breaking states in kagome metals.
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Submitted 22 January, 2025; v1 submitted 28 October, 2024;
originally announced October 2024.
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12-spin-qubit arrays fabricated on a 300 mm semiconductor manufacturing line
Authors:
Hubert C. George,
Mateusz T. Mądzik,
Eric M. Henry,
Andrew J. Wagner,
Mohammad M. Islam,
Felix Borjans,
Elliot J. Connors,
J. Corrigan,
Matthew Curry,
Michael K. Harper,
Daniel Keith,
Lester Lampert,
Florian Luthi,
Fahd A. Mohiyaddin,
Sandra Murcia,
Rohit Nair,
Rambert Nahm,
Aditi Nethwewala,
Samuel Neyens,
Bishnu Patra,
Roy D. Raharjo,
Carly Rogan,
Rostyslav Savytskyy,
Thomas F. Watson,
Josh Ziegler
, et al. (7 additional authors not shown)
Abstract:
Intels efforts to build a practical quantum computer are focused on developing a scalable spin-qubit platform leveraging industrial high-volume semiconductor manufacturing expertise and 300 mm fabrication infrastructure. Here, we provide an overview of the design, fabrication, and demonstration of a new customized quantum test chip, which contains 12-quantum-dot spin-qubit linear arrays, code name…
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Intels efforts to build a practical quantum computer are focused on developing a scalable spin-qubit platform leveraging industrial high-volume semiconductor manufacturing expertise and 300 mm fabrication infrastructure. Here, we provide an overview of the design, fabrication, and demonstration of a new customized quantum test chip, which contains 12-quantum-dot spin-qubit linear arrays, code named Tunnel Falls. These devices are fabricated using immersion and extreme ultraviolet lithography (EUV), along with other standard high-volume manufacturing (HVM) processes, as well as production-level process control. We present key device features and fabrication details, as well as qubit characterization results confirming device functionality. These results corroborate our fabrication methods and are a crucial step towards scaling of extensible 2D qubit array schemes.
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Submitted 20 December, 2024; v1 submitted 21 October, 2024;
originally announced October 2024.
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Charge density wave with suppressed long-range structural modulation in canted antiferromagnetic kagome FeGe
Authors:
Chenfei Shi,
Wenchang Hou,
Hanbin Deng,
Bikash Patra,
Surya Rohith Kotla,
Yi Liu,
Sitaram Ramakrishnan,
Claudio Eisele,
Harshit Agarwal,
Leila Noohinejad,
Ji-Yong Liu,
Tianyu Yang,
Guowei Liu,
Bishal Baran Maity,
Qi Wang,
Zhaodi Lin,
Baojuan Kang,
Wanting Yang,
Yongchang Li,
Zhihua Yang,
Yuxiang Chen,
Xiang Li,
Yuke Li,
Yanpeng Qi,
Arumugam Thamizhavel
, et al. (8 additional authors not shown)
Abstract:
Kagome lattice can host abundant exotic quantum states such as superconductivity and charge density wave (CDW). Recently, successive orders of A-type antiferromagnetism (AFM), CDW and canted AFM have been manifested upon cooling in kagome FeGe. However, the mechanism of CDW and interaction with magnetism remains unclear. Here we investigate the evolution of CDW with temperature across the canted A…
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Kagome lattice can host abundant exotic quantum states such as superconductivity and charge density wave (CDW). Recently, successive orders of A-type antiferromagnetism (AFM), CDW and canted AFM have been manifested upon cooling in kagome FeGe. However, the mechanism of CDW and interaction with magnetism remains unclear. Here we investigate the evolution of CDW with temperature across the canted AFM by single-crystal x-ray diffraction, scanning tunneling microscope (STM) and resonant elastic x-ray scattering (REXS). Interestingly, CDW-induced superlattice reflections become weak after the canted AFM, although long-range CDW order is still detectable by STM and REXS. We uncover a novel long-range CDW order with suppressed structural modulation, likely due to the competition for the underlying crystal structure between CDW and canted AFM. Additionally, occupational modulations of Ge1 in the kagome plane and displacive modulations of all atoms were extracted. The results confirm Ge dimerization along the c axis and suggest a dynamic transformation between different CDW domains.
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Submitted 14 July, 2025; v1 submitted 1 April, 2024;
originally announced April 2024.
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Topological surface states host superconductivity induced by the bulk condensate in YRuB$_2$
Authors:
Nikhlesh Singh Mehta,
Bikash Patra,
Mona Garg,
Ghulam Mohmad,
Mohd Monish,
Pooja Bhardwaj,
P. K. Meena,
K. Motla,
Ravi Prakash Singh,
Bahadur Singh,
Goutam Sheet
Abstract:
While the possibility of topological superconductivity (TSC) in hybrid heterostructures involving topologically nontrivial band structure and superconductors has been proposed, the realization of TSC in a single stoichiometric material is most desired for fundamental experimental investigation of TSC and its device applications. Bulk measurements on YRuB$_2$ detect a single superconducting gap of…
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While the possibility of topological superconductivity (TSC) in hybrid heterostructures involving topologically nontrivial band structure and superconductors has been proposed, the realization of TSC in a single stoichiometric material is most desired for fundamental experimental investigation of TSC and its device applications. Bulk measurements on YRuB$_2$ detect a single superconducting gap of $\sim$ 1 meV. This is supported by our electronic structure calculations which also reveal the existence of topological surface states in the system. We performed surface-sensitive Andreev reflection spectroscopy on YRuB$_2$ and detected the bulk superconducting gap as well as another superconducting gap of $\sim$ 0.5 meV. From our analysis of electronic structure, we show that the smaller gap is formed in the topological surface states in YRuB$_2$ due to the proximity of the bulk superconducting condensate. Thus, in agreement with the past theoretical predictions, we present YRuB$_2$ as a unique system that hosts superconducting topological surface states.
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Submitted 18 May, 2024; v1 submitted 15 September, 2023;
originally announced September 2023.
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Topological nonsymmorphic insulator versus Dirac semimetal in KZnBi
Authors:
Rahul Verma,
Bikash Patra,
Bahadur Singh
Abstract:
KZnBi was discovered recently as a new three-dimensional Dirac semimetal with a pair of bulk Dirac fermions in contrast to the $\mathbb{Z}_2$ trivial insulator reported earlier. In order to address this discrepancy, we have performed electronic structure and topological state analysis of KZnBi using the local, semilocal, and hybrid exchange-correlation (XC) functionals within the density functiona…
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KZnBi was discovered recently as a new three-dimensional Dirac semimetal with a pair of bulk Dirac fermions in contrast to the $\mathbb{Z}_2$ trivial insulator reported earlier. In order to address this discrepancy, we have performed electronic structure and topological state analysis of KZnBi using the local, semilocal, and hybrid exchange-correlation (XC) functionals within the density functional theory framework. We find that various XC functionals, including the SCAN meta-GGA and hybrid functional with 25\% Hartree-Fock (HF) exchange (HSE06), resolve a topological nonsymmorphic insulator state with the glide-mirror protected hourglass surface Dirac fermions. By carefully tuning the XC strength in modified Becke-Johnson (mBJ) potential, we recover the correct orbital ordering and Dirac semimetal state of KZnBi. We further show that increasing the default HF exchange in hybrid functional ($> 40\%$) can also capture the desired Dirac semimetal state with the correct orbital ordering of KZnBi. The calculated energy dispersion and carrier velocities of Dirac states are found to be in excellent agreement with the available experimental results. Our results demonstrate that KZnBi is a unique topological material where large XC effects are crucial to producing the Dirac semimetal state.
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Submitted 12 December, 2023; v1 submitted 11 September, 2023;
originally announced September 2023.
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Role of effective mass anisotropy in realizing a hybrid nodal-line fermion state
Authors:
Bikash Patra,
Rahul Verma,
Shin-Ming Huang,
Bahadur Singh
Abstract:
Understanding the role of lattice geometry in shaping topological states and their properties is of fundamental importance to condensed matter and device physics. Here we demonstrate how an anisotropic crystal lattice drives a topological hybrid nodal line in transition metal tetraphosphides $Tm$P$_4$ ($Tm$ = Transition metal). $Tm$P$_4$ constitutes a unique class of black phosphorus materials for…
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Understanding the role of lattice geometry in shaping topological states and their properties is of fundamental importance to condensed matter and device physics. Here we demonstrate how an anisotropic crystal lattice drives a topological hybrid nodal line in transition metal tetraphosphides $Tm$P$_4$ ($Tm$ = Transition metal). $Tm$P$_4$ constitutes a unique class of black phosphorus materials formed by intercalating transition metal ions between the phosphorus layers without destroying the characteristic anisotropic band structure of the black phosphorous. Based on the first-principles calculations and $k \cdot p$ theory, we show that $Tm$P$_4$ harbor a single hybrid nodal line formed between oppositely-oriented anisotropic $Tm~d$ and P states unhinged from the high-symmetry planes. The nodal line consists of both type-I and type-II nodal band crossings whose nature and location are determined by the effective-mass anisotropies of the intersecting bands. We further discuss a possible topological phase transition to exemplify the formation of the hybrid nodal line state in $Tm$P$_4$. Our results offer a comprehensive study for understanding the interplay between structural motifs-driven mass anisotropies and topology in anisotropic lattice materials to realize hybrid semimetal states.
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Submitted 25 December, 2023; v1 submitted 25 April, 2023;
originally announced April 2023.
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Realization of Z$_2$ Topological Metal in Single-Crystalline Nickel Deficient NiV$_2$Se$_4$
Authors:
Sitaram Ramakrishnan,
Shidaling Matteppanavar,
Andreas Schonleber,
Bikash Patra,
Birender Singh,
Arumugam Thamizhavel,
Bahadur Singh,
Srinivasan Ramakrishnan,
Sander van Smaalen
Abstract:
Temperature-dependent electronic and magnetic properties are reported for a Z2 topological metal single-crystalline nickel-deficient NiV$_2$Se$_4$. It is found to crystallize in the monoclinic Cr3S4 structure type with space group I2=m. From single-crystal x-ray diffraction, we find that there are vacancies on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our electron-pro…
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Temperature-dependent electronic and magnetic properties are reported for a Z2 topological metal single-crystalline nickel-deficient NiV$_2$Se$_4$. It is found to crystallize in the monoclinic Cr3S4 structure type with space group I2=m. From single-crystal x-ray diffraction, we find that there are vacancies on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our electron-probe microanalysis. The electrical resistivity shows metallic behavior with a broad anomaly around 150{200 K that is also observed in the heat capacity data. This anomaly indicates a change of state of the material below 150 K. We believe that this anomaly could be due to spin fluctuations or charge-density-wave (CDW) fluctuations, where the lack of long-range order is caused by vacancies at the Ni site of Ni0:85V2Se4. Although we fail to observe any structural distortion in this crystal down to 1.5 K, its electronic and thermal properties are anomalous. The observation of non-linear temperature dependence of resistivity as well as an enhanced value of the Sommerfeld coefficient = 104.0(1) mJ/molK2 suggests strong electron-electron correlations in this material. The first-principles calculations performed for NiV$_2$Se$_4$, which are also applicable to Ni0:85V2Se4, classify this material as a topological metal with Z2 = (1; 110) and coexisting electron and hole pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode, consistent with the absence of periodic lattice distortion in the present experiments.
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Submitted 18 April, 2023;
originally announced April 2023.
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Coexistence of phononic Weyl, nodal line, and threefold excitations in chalcopyrite CdGeAs$_{2}$ and associated thermoelectric properties
Authors:
Vikas Saini,
Bikash Patra,
Bahadur Singh,
A. Thamizhavel
Abstract:
Realization of topologically protected quantum states leads to unprecedented opportunities for fundamental science and device applications. Here, we demonstrate the coexistence of multiple topological phononic states and calculate the associated thermoelectric properties of a chalcopyrite material CdGeAs$_2$ using first-principles theoretical modeling. CdGeAs$_{2}$ is a direct bandgap semiconducto…
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Realization of topologically protected quantum states leads to unprecedented opportunities for fundamental science and device applications. Here, we demonstrate the coexistence of multiple topological phononic states and calculate the associated thermoelectric properties of a chalcopyrite material CdGeAs$_2$ using first-principles theoretical modeling. CdGeAs$_{2}$ is a direct bandgap semiconductor with a bandgap of $0.65$ eV. By analysing the phonon spectrum and associated symmetries, we show the presence of nearly isolated Weyl, nodal line, and threefold band crossings in CdGeAs$_2$. Specifically, the two triply degenerate points (TDPs) identified on the $k_{z}$ axis are formed by the optical phonons bands 7, 8, and 9 with type-II energy dispersion. These TDPs form a time reversal pair and are connected by a straight nodal line with zero Berry phase. The TDPs formed between bands 14, 15, and 16 exhibit type-I crossings and are connected through the open straight nodal line. Our transport calculations show a large thermopower exceeding $\sim$500 and $200$ $\rm μV/K$ for the hole and electron carriers, respectively, above 500 K with a carrier doping of 10$^{18}$ cm$^{-3}$. The large thermopower in $p$-type CdGeAs$_{2}$ is a consequence of the sharp density of states appear from the presence of a heavy hole band at the $Γ$ point. We argue that the presence of topological states in the phonon bands could lead to low lattice thermal conductivity and drive a high figure-of-merit in CdGeAs$_{2}$.
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Submitted 2 January, 2023;
originally announced January 2023.
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Coupling between colossal charge density wave ordering and magnetism in Ho2Ir3Si5
Authors:
Sitaram Ramakrishnan,
Jin-Ke Bao,
Claudio Eisele,
Bikash Patra,
Minoru Nohara,
Biplab Bag,
Leila Noohinejad,
Martin Tolkiehn,
Carsten Paulmann,
Achim M. Schaller,
Toms Rekis,
Surya Rohith Kotla,
Andreas Schönleber,
Arumugam Thamizhavel,
Bahadur Singh,
Srinivasan Ramakrishnan,
Sander van Smaalen
Abstract:
Ho2Ir3Si5 belongs to the family of three-dimensional (3D) R2Ir3Si5 (R = Lu, Er and Ho) compounds that exhibit a colossal first-order charge density wave (CDW) transition where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir-Ir zigzag chains along c are res…
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Ho2Ir3Si5 belongs to the family of three-dimensional (3D) R2Ir3Si5 (R = Lu, Er and Ho) compounds that exhibit a colossal first-order charge density wave (CDW) transition where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir-Ir zigzag chains along c are responsible for the CDW in all three compounds. The replacement of the rare earth element from non-magnetic Lu to magnetic Er or Ho lowers TCDW, where TCDWLu = 200 K, TCDWEr = 150 K and TCDWHo = 90 K. Out of the three compounds, Ho2Ir3Si5 is the only system where second-order superlattice reflections could be observed, indicative of an anharmonic shape of the modulation wave. The CDW transition is observed as anomalies in the temperature dependencies of the specific heat, electrical conductivity and magnetic susceptibility, which includes a large hysteresis of 90 to 130 K for all measured properties, thus corroborating the SXRD measurements. Similar to previously reported Er2Ir3Si5, there appears to be a coupling between CDW and magnetism such that the Ho3+ magnetic moments are influenced by the CDW transition, even in the paramagnetic state. Moreover, earlier investigations on polycrystalline material revealed antiferromagnetic (AFM) ordering at TN = 5.1 K, whereas AFM order is suppressed and only the CDW is present in our highly ordered single-crystal. First-principles calculations predict Ho2Ir3Si5 to be a metal with coexisting electron and hole pockets at the Fermi level. The Ho and Ir atoms have spherically symmetric metallic-type charge density distributions that are prone to CDW distortion. Phonon calculations affirm that the Ir atoms are primarily responsible for the CDW distortion, which is in agreement with the experiment.
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Submitted 28 October, 2022;
originally announced October 2022.
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Magnon bands in pyrochlore slabs with Heisenberg exchange and anisotropies
Authors:
V. V. Jyothis,
Bibhabasu Patra,
V. Ravi Chandra
Abstract:
The pyrochlore lattice is a versatile venue to probe the properties of magnetically ordered states induced or perturbed by anisotropic terms like the Dzyaloshinskii-Moriya interactions or single-ion anisotropy. Several such ordered states have been investigated recently as precursors of topological magnons and the associated surface states. In parallel, there has been recent progress in growing th…
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The pyrochlore lattice is a versatile venue to probe the properties of magnetically ordered states induced or perturbed by anisotropic terms like the Dzyaloshinskii-Moriya interactions or single-ion anisotropy. Several such ordered states have been investigated recently as precursors of topological magnons and the associated surface states. In parallel, there has been recent progress in growing thin films of magnetic materials with this lattice structure along high symmetry directions of the lattice. In both cases, an account of the magnetic excitations of relevant Hamiltonians for finite slabs is a necessary step in the analysis of the physics of these systems. We study here magnon bands in the slab geometry for a class of spin models on the pyrochlore lattice with Heisenberg exchange, Dzyaloshinskii-Moriya interaction and spin-ice anisotropy. For a range of model parameters, for both ferromagnetic and antiferromagnetic exchange, we compute the classical ground states for different slab orientations and determine the spin wave excitations above them. We analyze the ferromagnetic splay phase, the all-in-all-out phase and a coplanar phase and evaluate magnon dispersions for slabs oriented perpendicular to the $[111]$, $[100]$ and $[110]$ directions. For all the phases considered, depending on the slab orientation, magnon band structures can be non-reciprocal and we highlight the differences in the three orientations from this point-of-view. Finally, we present details of the surface localized magnons for all the three slab orientations in the phases we study. For the ferromagnetic splay phase and the all-in-all-out phase we analyze surface states associated with point degeneracies or nodal lines in the bulk spectrum by computing the magnonic Berry curvature and Weyl charges or Chern numbers associated with it.
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Submitted 22 February, 2024; v1 submitted 7 October, 2022;
originally announced October 2022.
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Intermittency of CsPbBr$_3$ perovskite quantum dots analyzed by an unbiased statistical analysis
Authors:
Isabelle M. Palstra,
Ilse Maillette de Buy Wenniger,
Biplab K. Patra,
Erik C. Garnett,
A. Femius Koenderink
Abstract:
We analyze intermittency in intensity and fluorescence lifetime of CsPbBr$_3$ perovskite quantum dots by applying unbiased Bayesian inference analysis methods. We apply changepoint analysis (CPA) and a Bayesian state clustering algorithm to determine the timing of switching events and the number of states between which switching occurs in a statistically unbiased manner, which we have benchmarked…
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We analyze intermittency in intensity and fluorescence lifetime of CsPbBr$_3$ perovskite quantum dots by applying unbiased Bayesian inference analysis methods. We apply changepoint analysis (CPA) and a Bayesian state clustering algorithm to determine the timing of switching events and the number of states between which switching occurs in a statistically unbiased manner, which we have benchmarked particularly to apply to highly multistate emitters. We conclude that perovskite quantum dots display a plethora of gray states in which brightness broadly speaking correlates inversely with decay rate, confirming the multiple recombination centers model. We leverage the CPA partitioning analysis to examine aging and memory effects. We find that dots tend to return to the bright state before jumping to a dim state, and that when choosing a dim state they tend to explore the entire set of states available.
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Submitted 5 May, 2021; v1 submitted 18 February, 2021;
originally announced February 2021.
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Cumulative effects of collision integral, strong magnetic field, and quasiparticle description on charge and heat transport in thermal QCD medium
Authors:
Salman Ahamad Khan,
Binoy Krishna Patra
Abstract:
Our first aim is to explore the effect of the collision integral with the insurance of instantaneous conservation of particle number on charge and heat transport in a thermal QCD medium. The second aim is to see how the dimensional reduction due to strong magnetic field (B) modulates the transport through the entangled effects, {\em such as} collision-time and occupation probability etc. in collis…
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Our first aim is to explore the effect of the collision integral with the insurance of instantaneous conservation of particle number on charge and heat transport in a thermal QCD medium. The second aim is to see how the dimensional reduction due to strong magnetic field (B) modulates the transport through the entangled effects, {\em such as} collision-time and occupation probability etc. in collision integral. The final aim is to check how the quasiparticle description through dispersion relation of thermal QCD in strong B, alters the aforesaid conclusions. We observe that modified collision term expedites both transport, which is manifested by large magnitudes of electrical ($σ_{\rm el}$) and thermal ($κ$) conductivities, in comparison to relaxation-collision term. As a corollary, Lorenz number is dominated by the later and Knudsen number is by the former. However, strong B not only flips the dominance of collision term in heat transport, it also causes drastic enhancement of both $σ_{\rm el}$ and $κ$ and reduction in specific heat. As a result, the equilibration factor, Knudsen number becomes much larger than one, which defies physical interpretation. Finally, quasiparticle description in the absence of strong B impedes the transport of charge and heat, resulting in the meagre decrease of conductivities, however, strong B does noticeable observations: conductivities now gets reduced to physically plausible values, T-dependence of $σ_{\rm el}$ gets reversed, {\em i.e.} it now decreases with T, effect of collision integral gets smeared in $κ$ etc. Knudsen number thus becomes much smaller than one, implying that the system be remained in equilibrium. These findings attribute to the fact that the collective modes in the dispersion relation of thermal QCD in strong B sets in much larger scale, manifested by large in-medium masses.
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Submitted 22 August, 2021; v1 submitted 5 November, 2020;
originally announced November 2020.
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CMOS-based cryogenic control of silicon quantum circuits
Authors:
Xiao Xue,
Bishnu Patra,
Jeroen P. G. van Dijk,
Nodar Samkharadze,
Sushil Subramanian,
Andrea Corna,
Charles Jeon,
Farhana Sheikh,
Esdras Juarez-Hernandez,
Brando Perez Esparza,
Huzaifa Rampurawala,
Brent Carlton,
Surej Ravikumar,
Carlos Nieva,
Sungwon Kim,
Hyung-Jin Lee,
Amir Sammak,
Giordano Scappucci,
Menno Veldhorst,
Fabio Sebastiano,
Masoud Babaie,
Stefano Pellerano,
Edoardo Charbon,
Lieven M. K. Vandersypen
Abstract:
The most promising quantum algorithms require quantum processors hosting millions of quantum bits when targeting practical applications. A major challenge towards large-scale quantum computation is the interconnect complexity. In current solid-state qubit implementations, a major bottleneck appears between the quantum chip in a dilution refrigerator and the room temperature electronics. Advanced l…
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The most promising quantum algorithms require quantum processors hosting millions of quantum bits when targeting practical applications. A major challenge towards large-scale quantum computation is the interconnect complexity. In current solid-state qubit implementations, a major bottleneck appears between the quantum chip in a dilution refrigerator and the room temperature electronics. Advanced lithography supports the fabrication of both CMOS control electronics and qubits in silicon. When the electronics are designed to operate at cryogenic temperatures, it can ultimately be integrated with the qubits on the same die or package, overcoming the wiring bottleneck. Here we report a cryogenic CMOS control chip operating at 3K, which outputs tailored microwave bursts to drive silicon quantum bits cooled to 20mK. We first benchmark the control chip and find electrical performance consistent with 99.99% fidelity qubit operations, assuming ideal qubits. Next, we use it to coherently control actual silicon spin qubits and find that the cryogenic control chip achieves the same fidelity as commercial instruments. Furthermore, we highlight the extensive capabilities of the control chip by programming a number of benchmarking protocols as well as the Deutsch-Josza algorithm on a two-qubit quantum processor. These results open up the path towards a fully integrated, scalable silicon-based quantum computer.
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Submitted 29 September, 2020;
originally announced September 2020.
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Magnetic field-induced anisotropic interaction in heavy quark bound states
Authors:
Salman Ahamad Khan,
Binoy Krishna Patra,
Mujeeb Hasan
Abstract:
We have investigated how a strong magnetic field (B) could decipher the anisotropic interaction in heavy quark ($Q$) and antiquark ($\bar Q$) bound states through the perturbative thermal QCD in real-time formalism. So we thermalize Schwinger propagator for quarks in LLL and the Feynman propagator for gluons to calculate the gluon self-energy. For the quark-loop contribution to the self-energy, th…
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We have investigated how a strong magnetic field (B) could decipher the anisotropic interaction in heavy quark ($Q$) and antiquark ($\bar Q$) bound states through the perturbative thermal QCD in real-time formalism. So we thermalize Schwinger propagator for quarks in LLL and the Feynman propagator for gluons to calculate the gluon self-energy. For the quark-loop contribution to the self-energy, the medium does not have any temperature correction and the vacuum term gives rise an anisotropic term whereas the gluon-loop yields temperature correction. This finding in quark-loop contribution corroborates the equivalence of a massless QED in (1+1)-dimension with the massless thermal QCD in strong B, which (quark sector) is reduced to (1+1)-dimension (longitudinal). Thus the permittivity of the medium behaves like as a tensor. Thus the permittivity of medium makes the $Q \bar Q$ potential anisotropic, which resembles with a contemporary results found in lattice studies. As a result, potential for $Q \bar Q$-pairs aligned transverse to B is more attractive than parallel alignment. However, potential is always more attractive compared to B=0 due to softening of screening mass. However, the imaginary-part of potential becomes smaller compared to B=0. We have next investigated the effects of strong ${\bf B}$ on binding energies (B.E.) and thermal widths ($Γ$) of ground states of $c \bar c$ and $b \bar b$ in a time-independent perturbation theory, where binding energies gets increased and widths gets decreased, compared to $B =0$. Finally we have studied the quasi-free dissociation of bound states in a strong B. The dissociation temperatures estimated for $J/ψ$ and $Υ$ states are obtained as $1.59 \rm{T_c} $ and $2.22 \rm{T_c}$, respectively, which are higher than the estimate in B=0 , thus preventing early dissolution of $Q \bar Q$ bound states.
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Submitted 19 April, 2020;
originally announced April 2020.
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Seebeck effect in a thermal QCD medium in the presence of strong magnetic field
Authors:
Debarshi Dey,
Binoy Krishna Patra
Abstract:
The strongly interacting partonic medium created post ultrarelativistic heavy ion collision experiments exhibits a significant temperature-gradient between the central and peripheral regions of the collisions, which in turn, is capable of inducing an electric field in the medium; a phenomenon known as Seebeck effect. The effect is quantified by the magnitude of the induced electric field per unit…
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The strongly interacting partonic medium created post ultrarelativistic heavy ion collision experiments exhibits a significant temperature-gradient between the central and peripheral regions of the collisions, which in turn, is capable of inducing an electric field in the medium; a phenomenon known as Seebeck effect. The effect is quantified by the magnitude of the induced electric field per unit temperature-gradient - the Seebeck coefficient ($S$). We study the coefficient, $S$ in the relativistic Boltzmann transport equation in relaxation-time approximation, as a function of temperature ($T$) and chemical potential ($μ$), wherein we find that with current quark masses, the magnitude of $S$ for individual flavours as well as that for the medium as a whole decreases with $T$ and increases with $μ$, with the electric charge of the flavour deciding the sign of $S$. The emergence of a strong magnetic field ($B$) in the non-central collisions at heavy-ion collider experiments motivates us to study the effect of $B$ on Seebeck effect. The strong $B$ affects $S$ in multifold ways, via : a) modification of phase-space due to the dimensional reduction, b) dispersion relation in lowest Landau level (occupation probability), and c) relaxation-time. We find that a strong $B$ not only decreases the magnitudes of $S$'s of individual species, it also flips their signs. This leads to a faster reduction of the magnitude of $S$ of the medium than its counterpart at $B=0$. We then explore how the interactions among partons in perturbative thermal QCD in the quasiparticle framework affect Seebeck effect, where we find that even in strong B, there is no more a flip of the sign of $S$ for individual species and an enhancement of the magnitudes of $S$ of individual species as well as that of the medium, compared to current quark mass description at either $B=0$ or $B \neq 0$.
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Submitted 6 November, 2020; v1 submitted 7 April, 2020;
originally announced April 2020.
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Thermomagnetic properties and Bjorken expansion of hot QCD matter in a strong magnetic field
Authors:
Shubhalaxmi Rath,
Binoy Krishna Patra
Abstract:
In this work we have studied the effects of an external strong magnetic field on the thermodynamic and magnetic properties of a hot QCD matter and then explored these effects on the subsequent hydrodynamic expansion of the said matter once produced in the ultrarelativistic heavy ion collisions. For that purpose, we have computed the quark and gluon self-energies up to one loop in the strong magnet…
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In this work we have studied the effects of an external strong magnetic field on the thermodynamic and magnetic properties of a hot QCD matter and then explored these effects on the subsequent hydrodynamic expansion of the said matter once produced in the ultrarelativistic heavy ion collisions. For that purpose, we have computed the quark and gluon self-energies up to one loop in the strong magnetic field, using the HTL approximation with two hard scales - temperature and magnetic field, which in turn compute the effective propagators for quarks and gluons, respectively. Hence the quark and gluon contributions to the free energy are obtained from the respective propagators and finally derive the equation of state (EOS) by calculating the pressure and energy density. We have found that the speed of sound is enhanced due to the presence of strong magnetic field and this effect will be later exploited in the hydrodynamics. Thereafter the magnetic properties are studied from the free energy of the matter, where the magnetization is found to increase linearly with the magnetic field, thus hints the paramagnetic behavior. The temperature dependence of the magnetization is also studied, where the magnetization is found to increase slowly with the temperature. Finally, to see how a strong magnetic field could affect the hydrodynamic evolution, we have revisited the Bjorken boost-invariant picture with our paramagnetic EOS as an input in the equation of motion for the energy-momentum conservation. We have noticed that the energy density evolves faster than in the absence of strong magnetic field, i.e. cooling becomes faster, which could have implications on the heavy-ion phenomenology. As mentioned earlier, this observation can be understood by the enhancement of the speed of sound.
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Submitted 6 February, 2019; v1 submitted 8 June, 2018;
originally announced June 2018.
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Is repulsion good for the health of Chimeras?
Authors:
Sarika Jalan,
Saptarshi Ghosh,
Bibhabasu Patra
Abstract:
Yes! Very much so.
A chimera state refers to the coexistence of a coherent-incoherent dynamical evolution of identically coupled oscillators. We investigate the impact of multiplexing of a lyer having repulsively coupled oscillators on occurrence of chimeras in the layer having attractively coupled identical oscillators. We report that there exists an enhancement in the appearance of chimera sta…
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Yes! Very much so.
A chimera state refers to the coexistence of a coherent-incoherent dynamical evolution of identically coupled oscillators. We investigate the impact of multiplexing of a lyer having repulsively coupled oscillators on occurrence of chimeras in the layer having attractively coupled identical oscillators. We report that there exists an enhancement in the appearance of chimera state in one layer of multiplex network in the presence of repulsive coupling in the other layer. Furthermore, we show that a small amount of inhibition or repulsive coupling in one layer is sufficient to yield chimera state in another layer by destroying its synchronized behavior. These results can be used to get insight into dynamical behaviors of those systems where both attractive and repulsive coupling exist among their constituents.
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Submitted 12 October, 2017; v1 submitted 11 October, 2017;
originally announced October 2017.
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Density matrix expansion based semi-local exchange hole applied to range separated density functional theory
Authors:
Bikash Patra,
Subrata Jana,
Prasanjit Samal
Abstract:
Exchange hole is the principle constituent in density functional theory, which can be used to accurately design exchange energy functional and range separated hybrid functionals coupled with some appropriate correlation. Recently, density matrix expansion (DME) based semi-local exchange hole proposed by Tao-Mo gained attention due to its fulfillment of some exact constraints. We propose a new long…
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Exchange hole is the principle constituent in density functional theory, which can be used to accurately design exchange energy functional and range separated hybrid functionals coupled with some appropriate correlation. Recently, density matrix expansion (DME) based semi-local exchange hole proposed by Tao-Mo gained attention due to its fulfillment of some exact constraints. We propose a new long-range corrected (LC) scheme that combines meta-generalized gradient approximation (meta-GGA) exchange functionals designed from DME exchange hole coupled with the ab-initio Hartree-Fock (HF) exchange integral by separating the Coulomb interaction operator using standard error function. Associate with Lee-Yang-Parr (LYP) correlation functional, assessment and benchmarking of our functional using well-known test set shows that it performs remarkably well for a broad range of molecular properties, such as thermochemistry, noncovalent interaction and barrier height of chemical reactions.
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Submitted 13 September, 2017;
originally announced September 2017.
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Performance of Range Separated Hybrids: Study within BECKE88 family and Semilocal Exchange Hole based Range Separated Hybrid
Authors:
Subrata Jana,
Bikash Patra,
Hemanadhan Myneni,
Prasanjit Samal
Abstract:
A long range corrected range separated hybrid functional is developed based on the density matrix expansion (DME) based semilocal exchange hole with Lee-Yang-Parr (LYP) correlation. An extensive study involving the proposed range separated hybrid for thermodynamic as well as properties related to the fractional occupation number is compared with different BECKE88 family semilocal, hybrid and range…
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A long range corrected range separated hybrid functional is developed based on the density matrix expansion (DME) based semilocal exchange hole with Lee-Yang-Parr (LYP) correlation. An extensive study involving the proposed range separated hybrid for thermodynamic as well as properties related to the fractional occupation number is compared with different BECKE88 family semilocal, hybrid and range separated hybrids. It has been observed that using Kohn-Sham kinetic energy dependent exchange hole several properties related to the fractional occupation number can be improved without hindering the thermochemical accuracy. The newly constructed range separated hybrid accurately describe the hydrogen and non-hydrogen reaction barrier heights. The present range separated functional has been constructed using full semilocal meta-GGA type exchange hole having exact properties related to exchange hole therefore, it has a strong physical basis.
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Submitted 1 September, 2017;
originally announced September 2017.