Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F22: Emerging Trends in MD Simulations and Machine Learning IIIFocus Session Live
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Sponsoring Units: DCOMP GDS DSOFT DPOLY Chair: Aiichiro Nakano, Univ of Southern California |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F22.00001: Machine learning assisted interatomic and electronic structure models for molecular simulation Invited Speaker: Linfeng Zhang We introduce a machine learning (ML)-based framework for building interatomic and electronic structure models following two general principles: 1) ML-based models should respect important physical constraints in a faithful and adaptive way; 2) to build truly reliable models, efficient algorithms are needed to explore relevant physical space and construct optimal training data sets. Two examples are given: 1) DeePMD, an end-to-end symmetry-preserving model for efficient molecular dynamics with ab initio accuracy; 2) DeePKS, a chemically accurate and widely-applicable electronic structure model within the framework of generalized Kohn-Sham density functional theory. If time permits, we will also present our efforts on developing related software packages and high-performance computing schemes, which have now been widely used worldwide by experts and practitioners in the molecular and materials simulation community. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F22.00002: WannierBerri code: High performance Wannier interpolation of Berry curvature and related quantities. Xiaoxiong Liu, Minsu Ghim, Patrick Lenggenhager, Miguel Ángel Jiménez Herrera, Iñigo Robredo, Ji Hoon Ryoo, Jae-Mo Lihm, Cheol-Hwan Park, Ivo Souza, Stepan Tsirkin We present WannierBerri (WB) [1] - a new Python code for Wannier interpolation. WB is close in spirit to the postprocessing module of the well-known Wannier90 code [2] (postw90.x), but improves over it by implementing a number of methodological advances [3]; these include a combination of fast and slow Fourier transforms, explicit use of symmetries and recursive adaptive grid refinement among others. These methods boost the speed of computations by orders of magnitude, enabling to study more complex materials with higher accuracy without demanding enormous computational resources. A plethora of quantities are implemented, such as anomalous Hall conductivity, orbital magnetization, Berry curvature dipole, and spin Hall conductivity, among many others. WB is also capable of evaluating analytical covariant derivatives of the Berry curvature and orbital moment, which allows to study different magnetotransport phenomena, and also to implement Fermi-sea formulations of Berry dipole. More features, such as Wilson loops, magnetoresistance, and electrical magneto-chiral anisotropy, are under active development, and WB aims to serve as a platform for developing new Wannier interpolation functionalities. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F22.00003: Systematic Comparison and Cross-validation of Fixed-Node Diffusion Monte Carloand Phaseless Auxiliary-Field Quantum Monte Carlo in Solids Anouar Benali, Fionn Malone, Miguel A Morales, Michel Caffarel, Paul Kent, Luke Shulenburger Diffusion Monte Carlo (DMC) and Auxiliary Field Quantum Monte Carlo (AFQMC) can both have their approximations systematically improved by applying successively more accurate trial wavefunctions. In this work we assess the feasibility of determining exact total energies for solid state Hamiltonians by studying primitive cells of four representative |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F22.00004: Prospects and Scaling Properties of Quantum Monte Carlo Forces for Heavier Ions Juha Tiihonen, Raymond Clay, Jaron Krogel Quantum Monte Carlo (QMC) forces are an important quantity for structural relaxation, force-field generation and studying, for instance, phonon interactions. However, they face well-known challenges due to difficult statistics [1] and Pulay corrections [2]. Powerful techniques exist to mitigate these problems, but the prospects of QMC forces in state-of-the-art applications remain somewhat uncharted. Here we give an outlook of continuum variational Monte Carlo and diffusion Monte Carlo forces in applications including heavier than usual elements, such as third row transition metals which require the use of pseudopotentials. We conclude by reporting the scaling properties of systematic errors and intrinsic variances of forces with the effective pseudopotential valence charge [3]. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F22.00005: Entanglement transitions as a probe of quasiparticles and quantum thermalization Tsung-Cheng Lu, Tarun Grover We introduce a diagnostic for quantum thermalization based on mixed-state entanglement. Specifically, given a pure state on a tripartite system ABC, we study the scaling of entanglement negativity between A and B. For representative states of self-thermalizing systems, either eigenstates or states obtained by a long-time evolution of product states, negativity shows a sharp transition from an area-law scaling to a volume-law scaling when the subsystem volume fraction is tuned across a finite critical value. In contrast, for a system with quasiparticles, it exhibits a volume-law scaling irrespective of the subsystem fraction. For many-body localized systems, the same quantity shows an area-law scaling for eigenstates, and volume-law scaling for long-time evolved product states, irrespective of the subsystem fraction. We provide a combination of numerical observations and analytical arguments in support of our conjecture. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F22.00006: MuST: A high performance ab initio framework for the study of disordered structures Yang Wang, Markus Eisenbach, Xianglin Liu, Mariia Karabin, Swarnava Ghosh, Hanna Terletska, Wasim Mondal, Ka-Ming Tam, Yi Zhang, Liviu Chioncel, Vishnu Raghuraman, Michael Widom, Fuyang Tian The effect of disorder in materials is of great fundamental and technological interest. In this presentation, I will introduce MuST, an open source package designed for enabling first principles investigation of disordered materials. MuST is developed based on full-potential multiple scattering theory with Green function approach, and is built upon decades of development of research codes that include KKR-CPA, a highly efficient ab initio method for the study of random alloys, and Locally Self-consistent Multiple Scattering (LSMS) method, a linear scaling ab initio code capable of treating extremely large disordered systems from the first principles using the largest parallel supercomputers available. Strong disorder and localization effects can also be studied in real system within the LSMS formalism with cluster embedding in an effective medium with the Typical Medium Dynamical Cluster Approximation (TMDCA), which enables a scalable approach for first principles studies of quantum materials. I will show the latest development of the MuST project, and discuss its potential applications and computational challenges. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F22.00007: A first-principles Quantum Monte Carlo study of two-dimensional (2D) GaSe and GaSe1-xSx alloys Daniel Wines, Kayahan Saritas, Can Ataca Two-dimensional (2D) post-transition metal chalcogenides (PTMCs) have attracted attention due to their suitable bandgaps and lower exciton binding energies. Of the predicted 2D PTMCs, GaSe has been reliably synthesized and experimentally characterized. Despite this fact, results vary depending on which density functional theory (DFT) functional is used. In an attempt to correct these discrepancies, we employed Diffusion Monte Carlo (DMC) to calculate the ground and excited state properties of GaSe because DMC has a weaker dependence on the trial wavefunction. We benchmark these results with experimental data, DFT and many-body perturbation theory (GW-BSE). We confirm that monolayer GaSe is an indirect gap semiconductor (Γ-M) with a quasiparticle gap in close agreement with experiment and low exciton binding energy. We also benchmark the optimal lattice parameter and cohesive energy with DMC and various DFT methods. In addition, we studied GaSe1-xSx alloyed structures (including Janus GaSSe) using QMC and tested the transferability of their optimized Jastrow parameters between different alloys. We aim to present a terminal theoretical benchmark for pristine monolayer GaSe and alloys, which will aid in the further study of 2D PTMCs and alloys using DMC methods. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F22.00008: Ensemble Green’s function theory for interacting electrons with degenerate ground states Erik Linnér, Ferdi Aryasetiawan In nature, correlated electronic systems containing degenerate ground states are common, with the degeneracy leading to fascinating phenomena such as the quantum Hall effect and emergent magnetic monopoles. Application of the Green’s function theory to degenerate systems has however not been extensively considered, in part stemming from the adiabatic connection being ambiguous for degenerate states. Current approaches either ignore the degeneracy or incorporate it in a non-generalizable manner. In our work [Phys. Rev. B 100, 235106 (2019)] we propose an ensemble Green’s function formalism, based on the von Neumann density matrix approach, for treating the one-electron excitation spectra of a degenerate electronic system. In the spirit of Hedin, we derive a set of iterative equations for the ensemble Green’s function and self-energy, and propose an 'ensemble GW' approximation, allowing for a well-defined treatment of degenerate electronic systems. The aim is to present the issues of degeneracy within the standard Green’s function method with focus on our proposed ensemble Green’s function method. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F22.00009: Boost all-electron full-potential DFT calculation with the domain specific SIRIUS library. Long Zhang, Samuel Trickey, H-P. Cheng We introduce the EXCITING-PLUS(EP) full potential linearized augmented plane wave (FP-LAPW) code interfaced with domain specific SIRIUS library. EP is a traditional FP-LAPW solide stated DFT code that suffers from the limitation of eigen system solver and non-distributed large data array. SIRIUS is a collection of common calculation elements within the family of pseudo potential plane wave DFT and FP-LAPW DFT. By abstracting and encapsulating the common objects SIRIUS can be interfaced with FP-LAPW codes like ELK and PP-PW codes like Quantum Esspresso. The library includes iterative type eigen system solver of the Davidson type, so that it can extend the ability of host code to deal with larger systems. We demonstrate the accuracy and efficiency of EP interfaced with SIRIUS. The interface improved the host code to handle larger systems. We tested small crystalline materials and got good accuracy in total energy and magnetic moment. We also tested magnetic molecules up to 100-200 atoms and got almost ideal scaling. The overall benchmark results show that SIRIUS is a powerful and efficient tool as a directly usable DFT-library rather than traditional algebra/math library. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F22.00010: Simulation of Quantum Spin-Liquid Phases with Spectral Methods Francisco Brito, Aires Ferreira In this work, we combine accurate Chebyshev polynomial expansions [1-3] and thermal pure quantum states (TPQ) [4] to simulate quantum spin models with highly entangled ground states. We use this hybrid framework to map out in a numerically exact fashion the phase diagram of the Kitaev-Heisenberg model on the honeycomb lattice [5]. Energy, magnetization and spin correlations are calculated with spectral accuracy in large systems with up to 24 spins. Our method can be easily extended to realistic spin models accommodating impurities, defects |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F22.00011: Excited states in variational Monte Carlo using a penalty method Shivesh Pathak, Brian Busemeyer, Jo?o N. B. Rodrigues, Lucas Wagner Finding excited states has been a long-standing challenge in variational Monte Carlo for interacting systems. While there has been notable progress on this front, existing algorithms either do not allow for optimization of all wave function parameters, can have trouble to converging to the correct state as recently shown by Filippi and coworkers, or miss degenerate states. We present an algorithm based on orthogonalization to the ground state that resolves these difficulties in the limit as the wave function parameterization becomes complete. We show an application to the benzene molecule, in which ~10,000 parameters are optimized for the first 12 excited states. |
Tuesday, March 16, 2021 2:06PM - 2:18PM Live |
F22.00012: Quantum Many-body Eigensolvers with Entanglement Renormalization Abid Khan, Xiongjie Yu, Bryan Clark, David Pekker We provide an approximate algorithm for computing eigenstates of Hamiltonians with hundreds of sites. |
Tuesday, March 16, 2021 2:18PM - 2:30PM Live |
F22.00013: Permutation Matrix Representation Quantum Monte Carlo Lalit Gupta, Tameem Albash, Itay Hen We present a quantum Monte Carlo algorithm for the simulation of general quantum and classical many-body models within a single unifying framework. The algorithm builds on a power series expansion of the quantum partition function in its off-diagonal terms and is both parameter-free and Trotter error-free. It allows for the study of a wide variety of models on an equal footing. We showcase the flexibility of our algorithm and the advantages it offers over existing state-of-the-art by simulating transverse- field Ising model Hamiltonians and comparing the performance of our technique against that of the stochastic series expansion algorithm. |
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