Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W59: Electronic Structure Methods I |
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Sponsoring Units: DCOMP Chair: Annabella Selloni, Princeton University Room: Room 301 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W59.00001: Tensor-based approach to accelerate exact exchange calculations in DFT Vishal Subramanian, Sambit Das, Vikram Gavini We propose a tensor structured approach based on systematically convergent Tucker-tensor decomposition to accelerate the evaluation of exact exchange functional in generalized Kohn-Sham (KS) density functional theory. In particular, the action of the Fock operator on the KS orbitals, which involves a convolution integral that is extended in real space, is reformulated as a tensor contraction involving quantities that are computed using convolution integrals in 1D. By exploiting various HPC strategies and optimal communication patterns, we have developed an efficient and scalable implementation on multi-core architectures. This approach, along with the ACE formulation, has been incorporated into DFT-FE, a finite-element-based DFT code. Benchmark studies involving Pt clusters show systematic convergence with an excellent agreement in the ground-state energies when compared to current state-of-the-art plane-wave DFT implementations. Further, we obtain a 3.5-7.5x speed up in the exact exchange computation in comparison to plane-wave DFT calculations, which translates to a 2-4x speed up in the full ground-state calculation for 38-88 atom Pt clusters. Notably, the speed up in the exact exchange computation increases with increasing system size, with an 11x speed up observed for a TiO2 cluster consisting of 480 atoms. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W59.00002: Real-Space, Real-Time Approach to Quantum Electrodynamical Density Functional Theory Justin M Malave, Alexander Ahrens, Daniel Pitagora, Cody Covington, Kalman Varga The quantum electrodynamical density functional theory (QED-DFT) is a powerful way to describe the interaction of light and matter in a fully quantum mechanical framework. In this talk a novel approach using a tensor product of a Fock space and real-space grid to solve QED-DFT is presented. The accuracy of this approach for molecules in cavities will be discussed. Examples include the coupling strength and or photon frequency dependence of numerous observables: ground state energies and densities; Rabi splitting magnitudes; optical absorption and high harmonic generation spectra in cavities; and photonic observables. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W59.00003: Velocity-gauge real-time density functional tight-binding method for large-scale systems Qiang Xu Real-time time-dependent density functional theory in the velocity gauge can probe the electronic excitations of solid-state systems; however, its immense computation cost makes it prohibitive for large systems. In this work, we developed an efficient velocity-gauge real-time method based on density functional tight-binding (VG-rtTDDFTB). We show that the VG-rtTDDFTB absorption spectrum and electron dynamics can generally reproduce the correct spectra for both molecular clusters and periodic systems. Furthermore, we show that the high efficiency of VG-rtTDDFTB allows the simulation of thousands of atoms (only 1 CPU core used), which provides a promising alternative for computing the electronic excitations of large systems. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W59.00004: Approximate range-separated DFT for the band structure of complex materials Thomas A Niehaus, Thomas Frauenheim, Tammo von der Heide, Balint Aradi, Ben Hourahine In recent years simulations based on range-separated exchange-correlation functionals in density functional theory have emerged as alternative to traditional GW and GW/BSE calculations in the determination of accurate quasi-particle band gaps [1] and excitonic features of materials [2]. Compared to local functionals, such computations are much more demanding in terms of computer time due to the incorporation of exact exchange. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W59.00005: Density functional approximations on the Quantum spin Hall insulator 1T’-WTe2 Li Yin, Hong Tang, Adrienn Ruzsinszky Quantum spin Hall insulators have attracted intensive experimental and theoretical studies due to its prosperous applications in spintronic devices. However, it’s challenging to accurately describe the electronic structure of the quantum spin Hall insulator via common density functional approximations. Only the Heyd-Scuseria-Ernzerhof (HSE06) with the aid of spin-orbit coupling and pseudo-potentials is effective to reveal the band opening in the typical quantum spin Hall insulator 1T’-WTe2, but with increased computational demands. Here, instead of the screened hybrid functional, we employ advanced meta-GGA density functional approximations to investigate the electronic structure of 1T’-WTe2, where the additionally introduced non-interacting kinetic energy density of the electron density make metal-GGAs flexible satisfying a greater number of exact constraints than common GGAs do. More specifically, the strongly-constrained and appropriately-normed (SCAN), regularized-restored SCAN (r2SCAN), meta-GGA made simple 2 (MS2), meta-GGA made very simple (MVS), TASK, and modified TASK (mTASK) approximations are utilized. We show that the TASK, mTASK, and MVS approximations are able to improve the band gap in 1T’-WTe2, as compared with common GGAs, highlighting the importance of meta-GGAs for quantum spin Hall insulators. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W59.00006: Finite difference interpolation for reduction of grid-related errors in Real Space Pseudopotential Density Functional Theory Deena Roller, Olle Hellman, Leeor Kronik The real-space pseudopotential approach is a well-known method for large-scale density functional theory (DFT) calculations. One of its main limitations, however, is the introduction of errors associated with the positioning of the underlying real-space grid, a phenomenon usually known as the ``egg-box'' effect. The effect can be controlled by using a finer grid, but this raises the cost of the calculations or even undermines their feasibility altogether. Therefore, there is ongoing interest in the reduction of the effect per a given real-space grid. Here, we present a finite difference interpolation of electron orbitals as a means of exploiting the high resolution of the pseudopotential to reduce egg-box effects systematically. We implement the method in PARSEC, a finite difference real-space pseudopotential DFT code, and demonstrate error mitigation and improved convergence at a low additional computational cost. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W59.00007: Hybrid functionals for heterogenous materials Jiawei Zhan, Marco Govoni, Giulia Galli Density Functional Theory provides a useful balance between accuracy and efficiency for electronic structure calculations of many molecules and solids. However, current exchange and correlation functionals, including semi-local and hybrid functionals, may be inaccurate in the description of the electronic properties of heterogeneous systems, especially interfaces between systems with large dielectric mismatch. Here, we present a dielectric-dependent range-separated hybrid functional for the investigation of heterogeneous materials, including surfaces and interfaces. Building on previous work [1], we define a spatial dependent fraction of exact exchange inspired bythe static Coulomb-hole and screened-exchange (COHSEX) approximation. We show that the proposed dielectric hybrid functional accurately predicts the electronic structure of several non-metallic interfaces, 2D systems, nanoparticles, defective solids,and molecular crystals. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W59.00008: Noncollinear relativistic Hubbard parameters and DFT+U with ultrasoft pseudopotentials Luca Binci, Nicola Marzari Density-functional theory (DFT) has proven to be an extremely successful theory to understand and predict ground state properties of real materials. However, it systematically fails when applied to systems in which the low-energy physics is characterized by localized electrons, for example with d or f character. To remedy this deficiency, Hubbard-augmented DFT functionals (e.g. DFT+U) have been developed in the last 30 years, and successfully applied to the study of weakly correlated oxides. In this work, we extend an implementation of the DFT+U functional in a plane-wave electronic structure code, from a scalar-relativistic to a fully-relativistic pseudopotential (FR-PP) framework. Our formulation is able to deal with FR-PP within the ultrasoft formalism, which allow an efficient plane-wave expansion of the pseudowavefunctions, especially when the electronic charge is heavily localized around the nuclei. We enhance our theory not only with total-energy, forces and stresses calculations, but we also develop a noncollinear linear-response approach based on density-functional perturbation theory which allow us to evaluate the interaction parameter U from first-principles, in an entirely parameter free scheme. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W59.00009: Real-space methods for electronic structure calculations of 100,000 atoms and beyond James R Chelikowsky, Mehmet Dogan, Kai-Hsin Liou With density functional theory and the use of pseudopotentials, the electronic structure problem can be effectively solved for many weakly coupled systems. However, computational cost of the Kohn–Sham equation is still a problem, frequently restricting the systems of interest to just a few thousand or fewer atoms. Here, we discuss novel methods that let us solve systems that contain more than 100,000 atoms. We concentrate on new computational algorithms based on real-space solutions of the Kohn-Sham equation. Our strategy has several benefits. First, the global communication required for fast Fourier transforms is avoided by real-space formalisms, such as finite differences and finite elements, which also provide superior scalability for big calculations across hundreds or thousands of computer nodes. Second, finite-difference techniques with a uniform real-space grid offer simple implementation; for instance, the grid spacing alone determines how quickly a Kohn-Sham solution converges. Based on a Chebyshev-filtered subspace iteration method, we developed a promising approach for solving the Kohn–Sham equations in real space [1–3]. We show with computations of confined systems with over 100,000 atoms or 400,000 electrons, that this method effectively reduces the communication overhead and improves the utilization of the vector processing capabilities provided by most modern parallel computers. We also describe our progress on even larger systems, surpassing 1,000,000 electrons. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W59.00010: The quantum-classical boundary in pharma-relevant quantum chemistry calculations Matthias Degroote, Joshua Goings, Alec F White, Joonho Lee, Christofer Tautermann, Craig M Gidney, Toru Shiozaki, Ryan Babbush, Nicholas C Rubin Chemical simulation is one of the most promising applications for future quantum computers. It is thought that quantum computers may enable accurate simulation for complex molecules that are otherwise impossible to simulate classically; that is, it displays quantum advantage. To better understand quantum advantage in chemical simulation, we explore what quantum and classical resources are required to simulate a series of pharmaceutically relevant molecules. Using classical methods, we show that reliable classical simulation of these molecules requires significant resources and therefore is a promising candidate for quantum simulation. We estimate the quantum resources, both in overall simulation time and the size. The insights from this study pave the way for future quantum simulation of complex molecules. |
Thursday, March 9, 2023 5:00PM - 5:12PM Author not Attending |
W59.00011: Snapshot-based detection of hidden off-diagonal long range order in fractional quantum hall states on lattices Fabian J Pauw, Sebastian Paeckel, Felix A Palm, Annabelle Bohrdt, Fabian Grusdt Revealing the existence of hidden off-diagonal long range order is believed to be a promising avenue towards identifying and characterizing topological order. In continuum fractional quantum Hall systems this can be accomplished by attaching gauge flux tubes onto the particles. Following the recent advances of cold atom experiments in optical lattices, probing this hidden, non-local order parameter with Fock-basis snapshots for lattice analogs is now within reach. Here, we demonstrate the existence of hidden off-diagonal long range order in quasi two-dimensional lattices in the ν=1/2-groundstate of the experimentally realistic isotropic Hofstadter-Bose-Hubbard model. To this end, we provide a MPS-driven, hybrid one and two-site snapshot procedure to sample the one-particle reduced density matrix and all particle positions simultaneously, emulating an experimentally feasible protocol. We present strong numerical indications for the emergence of an algebraic decay and discuss the resolution achievable using only few snapshots. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W59.00012: Midgap state requirements for optically active quantum defects Geoffroy Hautier, Yihuang Xiong, Milena Mathew, Sinead M Griffin, Alp Sipahigil Point defects in semiconducting hosts are promising for quantum information science (QIS). For instance, they can be used as spin-photon interfaces and a handful "quantum defects" are currently known and studied (e.g., NV center in diamond, T center in silicon, ...). A common criteria for the viability of such a "quantum defect" especially when studied through first principles computations is to require single particle defect states far from the band edges that can be excited by photons. Based on an analysis of currently studied quantum defects in silicon and diamond, we present evidences that such a model of two defect states far from the band edge might not be necessary. We argue that alternative electronic structures are viable as well and discuss their pros and cons. Our study refines the requirement necessary for viable quantum defects and will help the identification of new color centers for QIS using for instance first principles computations. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W59.00013: Photoemission spectroscopy from the three-body Green's function Arjan A Berger, gabriele riva, Pina Romaniello We present an original approach for the calculation of direct and inverse photo-emission spectra from first principles. |
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