Showing 1–12 of 12 results for author: Geng, D

Stable and Accurate Orbital-Free DFT Powered by Machine Learning

Authors: Roman Remme, Tobias Kaczun, Tim Ebert, Christof A. Gehrig, Dominik Geng, Gerrit Gerhartz, Marc K. Ickler, Manuel V. Klockow, Peter Lippmann, Johannes S. Schmidt, Simon Wagner, Andreas Dreuw, Fred A. Hamprecht

Abstract: Hohenberg and Kohn have proven that the electronic energy and the one-particle electron density can, in principle, be obtained by minimizing an energy functional with respect to the density. While decades of theoretical work have produced increasingly faithful approximations to this elusive exact energy functional, their accuracy is still insufficient for many applications, making it reasonable to… ▽ More Hohenberg and Kohn have proven that the electronic energy and the one-particle electron density can, in principle, be obtained by minimizing an energy functional with respect to the density. While decades of theoretical work have produced increasingly faithful approximations to this elusive exact energy functional, their accuracy is still insufficient for many applications, making it reasonable to try and learn it empirically. Using rotationally equivariant atomistic machine learning, we obtain for the first time a density functional that, when applied to the organic molecules in QM9, yields energies with chemical accuracy relative to the Kohn-Sham reference while also converging to meaningful electron densities. Augmenting the training data with densities obtained from perturbed potentials proved key to these advances. This work demonstrates that machine learning can play a crucial role in narrowing the gap between theory and the practical realization of Hohenberg and Kohn's vision, paving the way for more efficient calculations in large molecular systems. △ Less

Submitted 22 July, 2025; v1 submitted 1 March, 2025; originally announced March 2025.

Generalization of Urban Wind Environment Using Fourier Neural Operator Across Different Wind Directions and Cities

Authors: Cheng Chen, Geng Tian, Shaoxiang Qin, Senwen Yang, Dingyang Geng, Dongxue Zhan, Jinqiu Yang, David Vidal, Liangzhu Leon Wang

Abstract: Simulation of urban wind environments is crucial for urban planning, pollution control, and renewable energy utilization. However, the computational requirements of high-fidelity computational fluid dynamics (CFD) methods make them impractical for real cities. To address these limitations, this study investigates the effectiveness of the Fourier Neural Operator (FNO) model in predicting flow field… ▽ More Simulation of urban wind environments is crucial for urban planning, pollution control, and renewable energy utilization. However, the computational requirements of high-fidelity computational fluid dynamics (CFD) methods make them impractical for real cities. To address these limitations, this study investigates the effectiveness of the Fourier Neural Operator (FNO) model in predicting flow fields under different wind directions and urban layouts. In this study, we investigate the effectiveness of the Fourier Neural Operator (FNO) model in predicting urban wind conditions under different wind directions and urban layouts. By training the model on velocity data from large eddy simulation data, we evaluate the performance of the model under different urban configurations and wind conditions. The results show that the FNO model can provide accurate predictions while significantly reducing the computational time by 99%. Our innovative approach of dividing the wind field into smaller spatial blocks for training improves the ability of the FNO model to capture wind frequency features effectively. The SDF data also provides important spatial building information, enhancing the model's ability to recognize physical boundaries and generate more realistic predictions. The proposed FNO approach enhances the AI model's generalizability for different wind directions and urban layouts. △ Less

Submitted 9 January, 2025; originally announced January 2025.

Modeling Multivariable High-resolution 3D Urban Microclimate Using Localized Fourier Neural Operator

Authors: Shaoxiang Qin, Dongxue Zhan, Dingyang Geng, Wenhui Peng, Geng Tian, Yurong Shi, Naiping Gao, Xue Liu, Liangzhu Leon Wang

Abstract: Accurate urban microclimate analysis with wind velocity and temperature is vital for energy-efficient urban planning, supporting carbon reduction, enhancing public health and comfort, and advancing the low-altitude economy. However, traditional computational fluid dynamics (CFD) simulations that couple velocity and temperature are computationally expensive. Recent machine learning advancements off… ▽ More Accurate urban microclimate analysis with wind velocity and temperature is vital for energy-efficient urban planning, supporting carbon reduction, enhancing public health and comfort, and advancing the low-altitude economy. However, traditional computational fluid dynamics (CFD) simulations that couple velocity and temperature are computationally expensive. Recent machine learning advancements offer promising alternatives for accelerating urban microclimate simulations. The Fourier neural operator (FNO) has shown efficiency and accuracy in predicting single-variable velocity magnitudes in urban wind fields. Yet, for multivariable high-resolution 3D urban microclimate prediction, FNO faces three key limitations: blurry output quality, high GPU memory demand, and substantial data requirements. To address these issues, we propose a novel localized Fourier neural operator (Local-FNO) model that employs local training, geometry encoding, and patch overlapping. Local-FNO provides accurate predictions for rapidly changing turbulence in urban microclimate over 60 seconds, four times the average turbulence integral time scale, with an average error of 0.35 m/s in velocity and 0.30 °C in temperature. It also accurately captures turbulent heat flux represented by the velocity-temperature correlation. In a 2 km by 2 km domain, Local-FNO resolves turbulence patterns down to a 10 m resolution. It provides high-resolution predictions with 150 million feature dimensions on a single 32 GB GPU at nearly 50 times the speed of a CFD solver. Compared to FNO, Local-FNO achieves a 23.9% reduction in prediction error and a 47.3% improvement in turbulent fluctuation correlation. △ Less

Submitted 18 November, 2024; originally announced November 2024.

Realization of a two-dimensional checkerboard lattice in monolayer Cu$_2$N

Authors: Xuegao Hu, Run-Wu Zhang, Da-Shuai Ma, Zhihao Cai, Daiyu Geng, Zhenyu Sun, Qiaoxiao Zhao, Jisong Gao, Peng Cheng, Lan Chen, Kehui Wu, Yugui Yao, Baojie Feng

Abstract: Two-dimensional checkerboard lattice, the simplest line-graph lattice, has been intensively studied as a toy model, while material design and synthesis remain elusive. Here, we report theoretical prediction and experimental realization of the checkerboard lattice in monolayer Cu$_2$N. Experimentally, monolayer Cu$_2$N can be realized in the well-known N/Cu(100) and N/Cu(111) systems that were prev… ▽ More Two-dimensional checkerboard lattice, the simplest line-graph lattice, has been intensively studied as a toy model, while material design and synthesis remain elusive. Here, we report theoretical prediction and experimental realization of the checkerboard lattice in monolayer Cu$_2$N. Experimentally, monolayer Cu$_2$N can be realized in the well-known N/Cu(100) and N/Cu(111) systems that were previously mistakenly believed to be insulators. Combined angle-resolved photoemission spectroscopy measurements, first-principles calculations, and tight-binding analysis show that both systems host checkerboard-derived hole pockets near the Fermi level. In addition, monolayer Cu$_2$N has outstanding stability in air and organic solvents, which is crucial for further device applications. △ Less

Submitted 8 June, 2023; originally announced June 2023.

Comments: Nano Letters, in press

Observation of Gapped Dirac Cones in a Two-Dimensional Su-Schrieffer-Heeger Lattice

Authors: Daiyu Geng, Hui Zhou, Shaosheng Yue, Zhenyu Sun, Peng Cheng, Lan Chen, Sheng Meng, Kehui Wu, Baojie Feng

Abstract: The Su-Schrieffer-Heeger (SSH) model in a two-dimensional rectangular lattice features gapless or gapped Dirac cones with topological edge states along specific peripheries. While such a simple model has been recently realized in photonic/acoustic lattices and electric circuits, its material realization in condensed matter systems is still lacking. Here, we study the atomic and electronic structur… ▽ More The Su-Schrieffer-Heeger (SSH) model in a two-dimensional rectangular lattice features gapless or gapped Dirac cones with topological edge states along specific peripheries. While such a simple model has been recently realized in photonic/acoustic lattices and electric circuits, its material realization in condensed matter systems is still lacking. Here, we study the atomic and electronic structure of a rectangular Si lattice on Ag(001) by angle-resolved photoemission spectroscopy and theoretical calculations. We demonstrate that the Si lattice hosts gapped Dirac cones at the Brillouin zone corners. Our tight-binding analysis reveals that the Dirac bands can be described by a 2D SSH model with anisotropic polarizations. The gap of the Dirac cone is driven by alternative hopping amplitudes in one direction and staggered potential energies in the other one and hosts topological edge states. Our results establish an ideal platform to explore the rich physical properties of the 2D SSH model. △ Less

Submitted 12 October, 2022; originally announced October 2022.

Comments: Accepted for publication in Nature Communications

Journal ref: Nat. Commun. 13, 7000 (2022)

Observation of topological flat bands in the kagome semiconductor Nb$_3$Cl$_8$

Authors: Zhenyu Sun, Hui Zhou, Cuixiang Wang, Shiv Kumar, Daiyu Geng, Shaosheng Yue, Xin Han, Yuya Haraguchi, Kenya Shimada, Peng Cheng, Lan Chen, Youguo Shi, Kehui Wu, Sheng Meng, Baojie Feng

Abstract: The destructive interference of wavefunctions in a kagome lattice can give rise to topological flat bands (TFBs) with a highly degenerate state of electrons. Recently, TFBs have been observed in several kagome metals, including Fe$_3$Sn$_2$, FeSn, CoSn, and YMn$_6$Sn$_6$. Nonetheless, kagome materials that are both exfoliable and semiconducting are lacking, which seriously hinders their device app… ▽ More The destructive interference of wavefunctions in a kagome lattice can give rise to topological flat bands (TFBs) with a highly degenerate state of electrons. Recently, TFBs have been observed in several kagome metals, including Fe$_3$Sn$_2$, FeSn, CoSn, and YMn$_6$Sn$_6$. Nonetheless, kagome materials that are both exfoliable and semiconducting are lacking, which seriously hinders their device applications. Herein, we show that Nb$_3$Cl$_8$, which hosts a breathing kagome lattice, is gapped out because of the absence of inversion symmetry, while the TFBs survive because of the protection of the mirror reflection symmetry. By angle-resolved photoemission spectroscopy measurements and first-principles calculations, we directly observe the TFB and a moderate band gap in Nb$_3$Cl$_8$. By mechanical exfoliation, we successfully obtain monolayers of Nb$_3$Cl$_8$ and confirm that they are stable under ambient conditions. In addition, our calculations show that monolayers of Nb$_3$Cl$_8$ have a magnetic ground state, thus providing opportunities to study the interplay between geometry, topology, and magnetism. △ Less

Submitted 8 June, 2022; v1 submitted 2 November, 2021; originally announced November 2021.

Comments: 6 pages, 4 figures

Journal ref: Nano Lett. 22, 4596 (2022)

Observation of one-dimensional Dirac fermions in silicon nanoribbons

Authors: Shaosheng Yue, Hui Zhou, Ya Feng, Yue Wang, Zhenyu Sun, Daiyu Geng, Masashi Arita, Shiv Kumar, Kenya Shimada, Peng Cheng, Lan Chen, Yugui Yao, Sheng Meng, Kehui Wu, Baojie Feng

Abstract: Dirac materials, which feature Dirac cones in the reciprocal space, have been one of the hottest topics in condensed matter physics in the past decade. To date, 2D and 3D Dirac Fermions have been extensively studied, while their 1D counterparts are rare. Recently, Si nanoribbons (SiNRs), which are composed of alternating pentagonal Si rings, have attracted intensive attention. However, the electro… ▽ More Dirac materials, which feature Dirac cones in the reciprocal space, have been one of the hottest topics in condensed matter physics in the past decade. To date, 2D and 3D Dirac Fermions have been extensively studied, while their 1D counterparts are rare. Recently, Si nanoribbons (SiNRs), which are composed of alternating pentagonal Si rings, have attracted intensive attention. However, the electronic structure and topological properties of SiNRs are still elusive. Here, by angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy measurements, first-principles calculations, and tight-binding model analysis, we demonstrate the existence of 1D Dirac Fermions in SiNRs. Our theoretical analysis shows that the Dirac cones derive from the armchairlike Si chain in the center of the nanoribbon and can be described by the Su-Schrieffer-Heeger model. These results establish SiNRs as a platform for studying the novel physical properties in 1D Dirac materials. △ Less

Submitted 13 May, 2022; v1 submitted 6 October, 2021; originally announced October 2021.

Comments: 4 figures

Journal ref: Nano Lett. 22, 695-701 (2022)

Topological electronic structure in the antiferromagnet HoSbTe

Authors: Shaosheng Yue, Yuting Qian, Meng Yang, Daiyu Geng, Changjiang Yi, Shiv Kumar, Kenya Shimada, Peng Cheng, Lan Chen, Zhijun Wang, Hongming Weng, Youguo Shi, Kehui Wu, Baojie Feng

Abstract: Magnetic topological materials, in which the time-reversal symmetry is broken, host various exotic quantum phenomena, including the quantum anomalous Hall effect, axion insulator states, and Majorana fermions. The study of magnetic topological materials is at the forefront of condensed matter physics. Recently, a variety of magnetic topological materials have been reported, such as Mn$_3$Sn, Co… ▽ More Magnetic topological materials, in which the time-reversal symmetry is broken, host various exotic quantum phenomena, including the quantum anomalous Hall effect, axion insulator states, and Majorana fermions. The study of magnetic topological materials is at the forefront of condensed matter physics. Recently, a variety of magnetic topological materials have been reported, such as Mn$_3$Sn, Co$_3$Sn$_2$S$_2$, Fe$_3$Sn$_2$, and MnBi$_2$Te$_4$. Here, we report the observation of a topological electronic structure in an antiferromagnet, HoSbTe, a member of the ZrSiS family of materials, by angle-resolved photoemission spectroscopy measurements and first-principles calculations. We demonstrate that HoSbTe is a Dirac nodal line semimetal when spin-orbit coupling (SOC) is neglected. However, our theoretical calculations show that the strong SOC in HoSbTe fully gaps out the nodal lines and drives the system to a weak topological insulator state, with each layer being a two-dimensional topological insulator. Because of the strong SOC in HoSbTe, the gap is as large as hundreds of meV along specific directions, which is directly observed by our ARPES measurements. The existence of magnetic order and topological properties in HoSbTe makes it a promising material for realization of exotic quantum devices. △ Less

Submitted 7 October, 2020; originally announced October 2020.

Comments: 5 pages, 3 figures

Journal ref: Phys. Rev. B 102, 155109 (2020)

Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

Authors: A. G. Basden, D. Atkinson, N. A. Bharmal, U. Bitenc, M. Brangier, T. Buey, T. Butterley, D. Cano, F. Chemla, P. Clark, M. Cohen, J. -M. Conan, F. J. de Cos, C. Dickson, N. A. Dipper, C. N. Dunlop, P. Feautrier, T. Fusco, J. L. Gach, E. Gendron, D. Geng, S. J. Goodsell, D. Gratadour, A. H. Greenaway, A. Guesalaga , et al. (34 additional authors not shown)

Abstract: Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time c… ▽ More Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time control systems of two wide-field AO systems. These are CANARY, which has been operating on-sky since 2010, and DRAGON, which is a laboratory adaptive optics real-time demonstrator instrument. We detail the issues and difficulties that arose, along with the solutions we developed. We also provide recommendations for consideration when developing future wide-field AO systems. △ Less

Submitted 24 March, 2016; originally announced March 2016.

Comments: Accepted for publication in MNRAS

Vacuum ultraviolet photon detector with continuously adjustable resolution for inverse photoemission spectroscopy

Authors: Shu-Hu Liu, Cai-Hao Hong, Yi-Dong Zhao, Dong-Ping Geng, Lei Zheng, Xiao-Liang Zhao, Hua-Peng Li

Abstract: We present a vacuum ultraviolet (VUV) band-pass photon detector for inverse photoemission spectroscopy. A SrF2 window is used due to its high-energy cutoff of the optical transmission being 9.7eV, and acetone is selected as filling gas with the photoionization threshold also being 9.7eV. The structure of the detector described in detail is based on a Geiger-Müller type counter with an MgF2 window… ▽ More We present a vacuum ultraviolet (VUV) band-pass photon detector for inverse photoemission spectroscopy. A SrF2 window is used due to its high-energy cutoff of the optical transmission being 9.7eV, and acetone is selected as filling gas with the photoionization threshold also being 9.7eV. The structure of the detector described in detail is based on a Geiger-Müller type counter with an MgF2 window and argon as amplification gas. Its energy resolution can be tuned continuously from 46meV with a normal temperature situation to 105meV at 215K. Meanwhile, the signal intensity of the detector is adjusted accordingly to find an optimal operation program for our inverse photoemission system which is being constructed. The ratio of acetone vapor and argon is varied carefully. Background signals and the response of time are analyzed. The detector is normalized by deuterium lamp in combination with a grating monochromator. △ Less

Submitted 4 June, 2015; v1 submitted 12 November, 2014; originally announced November 2014.

Comments: This paper has been withdrawn by the author due to the confusing layout in the whole article

The Durham adaptive optics real-time controller

Authors: Alastair Basden, Deli Geng, Richard Myers, Eddy Younger

Abstract: The Durham adaptive optics real-time controller was initially a proof of concept design for a generic adaptive optics control system. It has since been developed into a modern and powerful CPU based real-time control system, capable of using hardware acceleration (including FPGAs and GPUs), based primarily around commercial off the shelf hardware. It is powerful enough to be used as the real-time… ▽ More The Durham adaptive optics real-time controller was initially a proof of concept design for a generic adaptive optics control system. It has since been developed into a modern and powerful CPU based real-time control system, capable of using hardware acceleration (including FPGAs and GPUs), based primarily around commercial off the shelf hardware. It is powerful enough to be used as the real-time controller for all currently planned 8~m class telescope adaptive optics systems. Here we give details of this controller and the concepts behind it, and report on performance including latency and jitter, which is less than 10~$μ$s for small adaptive optics systems. △ Less

Submitted 15 October, 2010; originally announced October 2010.

Comments: Accepted for publication in applied optics

Shack-Hartmann sensor improvement using optical binning

Authors: Alastair Basden, Deli Geng, Dani Guzman, Tim Morris, Richard Myers, Chris Saunter

Abstract: We present a design improvement for a recently proposed type of Shack-Hartmann wavefront sensor that uses a cylindrical (lenticular) lenslet array. The improved sensor design uses optical binning and requires significantly fewer detector pixels than the corresponding conventional or cylindrical Shack-Hartmann sensor, and so detector readout noise causes less signal degradation. Additionally, det… ▽ More We present a design improvement for a recently proposed type of Shack-Hartmann wavefront sensor that uses a cylindrical (lenticular) lenslet array. The improved sensor design uses optical binning and requires significantly fewer detector pixels than the corresponding conventional or cylindrical Shack-Hartmann sensor, and so detector readout noise causes less signal degradation. Additionally, detector readout time is significantly reduced, which reduces the latency for closed loop systems, and data processing requirements. We provide simple analytical noise considerations and Monte-Carlo simulations, and show that the optically binned Shack-Hartmann sensor can offer better performance than the conventional counterpart in most practical situations, and our design is particularly suited for use with astronomical adaptive optics systems. △ Less

Submitted 19 July, 2007; originally announced July 2007.

Comments: Accepted for publication in Applied Optics