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 Y59: Electronic Structure Methods II |
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Sponsoring Units: DCOMP Chair: Annabella Selloni, Princeton University Room: Room 301 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y59.00001: Extracting Excited States Energies from a Density Functional Database. Jose Gustavo Bravo Flores, Mark R Pederson, Koblar A Jackson, Kushantha Withanage, Alexander I Johnson The development of new computational tools is greatly helped by testing any new method on small and well-known systems, such as rare earth atoms, whose properties are well established through experiments and calculations, such as density functional theory (DFT). Such calculations can run fairly faster than those of molecules or clusters. Here we present a method for approaching configuration interaction accuracy by analyzing all the non self consistent data that is encountered during the path to self consistency. Our results have employed density functional approximations but our method can use data from any and all single determinantal data base(s). Applications of our method to core and valence level excitations of rare earth atoms are presented. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y59.00002: Symmetry-breaking origins of the high thermoelectric performance of Ge 1-xMnxTe alloys Ferdaushi A Bipasha, Jesse M Adamczyk, Eric S Toberer, Elif Ertekin GeTe is a well-known thermoelectric material that undergoes a phase transition from rhombohedral to rock salt phase and shows improved thermoelectric performance when alloyed with Mn. To understand the root causes of this high performance in Ge1-xMnxTe alloys, computational modeling can provide an in-depth view of structural and electronic properties. In this work, we use first-principles calculations and alloy modeling techniques to analyze fully disordered alloys in both the rhombohedral and rock salt phases to understand the structural transition, redistribution of bond lengths, and effective electronic structure. Our analysis indicates the thermodynamic stability of the rock salt phase over the rhombohedral phase with increased Mn content due to the absence of lone pair electrons in Mn. We observe band convergence and the emergence of new valence band maxima (VBM) with moderate Mn content around 12.5% near the phase transition, that may be related to the improved thermoelectric properties. However, additional Mn content creates dispersion-less flat bands and strong smearing near VBM. Experimental measurements show increase in effective mass, reduction in mobility with increasing Mn content, and minimum thermal conductivity near the phase transition. We conclude that good thermoelectric properties are achievable in Ge1-xMnxTe alloys at compositions close to the phase transition with moderate Mn content due to band convergence, moderate effective mass, and favorable transport properties. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y59.00003: Fermi surfaces from many body ground states: theory and application to PdCoO2 Jaron T Krogel, Abdulgani Annaberdiyev, Panchapakesan Ganesh The electronic Fermi surface is an object of fundamental interest in many sub-fields of condensed matter physics, with central relevance to an understanding of electronic conduction, charge density wave physics, and topological properties. We derive a connection between the momentum distribution backfolding procedure of Lock, Crisp, and West with the eigenvalues of the one body reduced density matrix of an interacting ground state wavefunction. Finite discontinuities in the resulting occupation number distribution in the first Brillouin zone gives direct access to the structure of the Fermi surface for both simple and correlated metals. We demonstrate this connection in the high mobility quasi-2D conductor PdCoO2 via direct comparison between ARPES and the Fermi surface obtained by many body quantum Monte Carlo techniques. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y59.00004: Optical and Electronic Properties of LiCoO2: Using multideterminant methods and quantum Monte Carlo to characterize a strongly correlated material Kevin Gasperich, Hyeondeok Shin, Tomas Rojas Solorzano, Jaron T Krogel, Anh T Ngo, Anouar Benali Understanding and accounting for strong correlations in ab initio simulations is essential for predicting properties of novel materials. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y59.00005: Surface Green function method for inhomogeneous multilayered systems Hunter Sims, Eli Hellmig, Tom Berlijn Inhomogeneous multilayered structures – e.g., interfaces between bulk substrates and one or more monolayered materials, van-der-Waals heterostructures, and Janus particles – exhibit electronic and magnetic properties that depend not only on the identity of the surface layer but on the neighboring environment. This remains true in structures containing 2D materials such as graphene and MoS2. Calculating the surface electronic structure of such systems is complicated by both the need for periodic simulation cells in most first-principles approaches and the assumption of homogeneity in existing codes that compute surface Green functions and/or simulate ARPES experiments. Using DFT+Wannier90 tight-binding Hamiltonians as a starting point, we have generalized the method of López Sancho et al. to allow for inhomogeneous layered structures and present calculations of the surface electronic spectra of monolayer FeSe on SrTiO3 as well as systems containing MoSe2 / MoS2 interfaces. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y59.00006: Band structures of 2D transition metal dichalcogenides from fully relativistic Dirac--Kohn--Sham theory using Gaussian-type orbitals Marius Kadek, Baokai Wang, Marc Joosten, Wei-Chi Chiu, Francois Mairesse, Michal Repisky, Kenneth Ruud, Arun Bansil I will present first-principles studies of spin-orbit-driven features, such as the Rashba splitting and Z2 topological invariant, of band structures of 2D transition metal dichalcogenides in 2H, 1T, and 1T' structural phases obtained from the fully relativistic Dirac-Kohn-Sham theory based on the Gaussian-type orbitals. I will discuss methodological adaptations enabling smooth parallelization and convergence of the electronic structure solver in cases where diffuse functions cause linear dependancies of basit sets. The presented method does not employ pseudopotentials and describes all electronic states on equal footing - enabling direct studies of material properties that originate in the relativistic theory and depend heavily on the electron density near nuclei, such as the spin Hamiltonian parameters. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y59.00007: Model selection in atomistic simulation Jonathan E Moussa There are many atomistic simulation methods with very different costs, accuracies, transferabilities, and numbers of empirical parameters. I show how statistical model selection can compare these methods fairly, even when they are very different. These comparisons are also useful for developing new methods that balance cost and accuracy. As an example, I build a semiempirical model for hydrogen clusters. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y59.00008: The effect of strong light-matter interaction on single-molecular reactions Robert L Smith, Fabijan Pavosevic, Angel Rubio Strong light-matter interactions can either suppress or enhance molecular reactions on the mesoscale. Ab initio quantum electrodynamics methods must be employed to understand the influence of cavity confinement on a single-molecular reaction. Quantum electrodynamics coupled cluster (QED-CC) is one such method where both bosons and fermions can be treated on equal footing quantum mechanically. In this talk, QED-CC is used to elucidate the contribution of strong light-matter interactions on the catalysis of some selected cycloaddition and substitution reactions confined to an optical cavity. The cycloaddition reactions yield a mixture of stereoisomers under typical reaction conditions; however, we demonstrate catalysis dependent on the molecular orientation inside the cavity, which yields a chosen stereoisomer product on demand. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y59.00009: Band Gap Problem Caused by Widespread Errors in Calculations and not by Density Functional Theory (DFT) YURIY MALOZOVSKY, Diola Bagayoko, Yacouba Issa Diakite The second theorem of Density functional theory (DFT) is clear: To obtain results that possess the full, physical content of DFT, an electronic structure calculation must utilize the ground state charge density in order to reach the ground state energy. This three-dimensional charge density is à priori unknown. Consequently, electronic structure calculations must perform a generalized minimization of the energy functional, using successive, self-consistent calculations with augmented basis sets, to reach the absolute minima of the occupied energies, i.e., the ground state. Then, the first or smallest of the basis sets that lead to the ground state produces the ground state charge density upon reaching self-consistency. The mainstream practice of selecting a single basis set and of performing iterations to reach a stationary state mistakenly consider that state to be the ground state. We prove, with the Rayleigh theorem for eigenvalues and the second DFT theorem, that it is not. In doing so, we show that the widespread disagreement between the results of “DFT calculations” and corresponding experimental ones cannot be ascribed to DFT. With the correct, computational method, we have described and predicted electronic and related properties of over 25 semiconductors, including their band gaps that were underestimated by 400 previous DFT calculations. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y59.00010: Hybrid Auxiliary Field Quantum Monte Carlo for molecular systems Yixiao Chen, Linfeng Zhang, Weinan E, Roberto Car We propose a quantum Monte Carlo approach to solve the ground state many-body Schrodinger equation for the electronic ground state. The method combines optimization from variational Monte Carlo and propagation from auxiliary field quantum Monte Carlo. It gives highly accurate results in molecular test cases, before the fermionic sign problem sets in. We obtain uniform accuracy for configurations near and far from equilibrium, that are dominated by dynamic and static correlations, respectively. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y59.00011: Probing the structure and phonon properties of solids with auxiliary-field quantum Monte Carlo Siyuan Chen, Shiwei Zhang Determining the accurate structure of a material is a critical step in understanding its physics. Predictive computations in correlated materials remain a major challenge. We present a direct, ab initio computation of forces and stresses with auxiliary-field quantum Monte Carlo (AFQMC) using planewave basis and multiple projector pseudopotentials. Our method potentially allows determination of the potential energy surface at a much higher efficiency than an approach based on total energies alone. In addition, we propose a fast and robust structural optimization algorithm [1] for optimizations when the forces or gradients are statistically noisy. Applying this algorithm in combination with forces and stresses computed by AFQMC, we demonstrate efficient, accurate, and full degrees-of-freedom optimizations in solids. Furthermore, we show that the AFQMC forces can be used to obtain accurate phonon spectra in solids. |
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