Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S31: Wavefunction Methods (ES3)Focus
|
Hide Abstracts |
Sponsoring Units: DCP Chair: James Shepherd Room: BCEC 203 |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S31.00001: The lord of the rings and ladders applied to solids and surfaces Invited Speaker: Andreas Grueneis This presentation will review recent progress in applying periodic coupled cluster theories to the study of surfaces and solids. We will discuss methods that reduce the computational cost and accelerate convergence of calculated properties towards the complete basis set as well as thermodynamic limit. These recent developments have enabled an increasing number of ab-initio studies and allowed for assessing the accuracy of coupled cluster theories by comparing to experimental findings as well as quantum Monte Carlo results. The presented applications will include phase diagrams of solids and molecular adsorption energies. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S31.00002: Localized active-space self-consistent field method: a size-extensive, linear-scaling MC-SCF approach for strongly-correlated materials Matthew Hermes, Laura Gagliardi The complete active space (CAS) SCF method and its perturbative corrections are the standard computational strategy in the field of quantum chemistry for computing accurate wave functions of strongly-correlated molecular systems. They are, however, not applicable to materials in a condensed phase because they are not size extensive and/or have exponential cost scaling, and common cost-controlling approximations such as restricted or generalized active space (RAS, GAS) do not resolve this difficulty. However, our recently-developed localized active space (LAS) SCF method, which is based on a union of density matrix embedding theory (DMET) and MC-SCF concepts, generates a wave function which, unlike RAS or GAS, is multiplicatively separable between disjoint, real-space-localized active subspaces. LASSCF is therefore both size consistent and size extensive, and in principle, its computational cost is linear scaling with respect to system size. We test this method on various realistic chemical models of strongly-correlated systems and show that LASSCF gives CASSCF-quality results, implying an attractive possibility for computing wave functions of strongly-correlated condensed systems. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S31.00003: Transitioning High-Accuracy Electronic Structure Methods from Molecules to the Solid State Malte Lange, Timothy Berkelbach This presentation discusses ongoing work to transfer trusted computational and theoretical tools that are traditionally used in the molecular regime to the rapidly growing field of solid state physics. Specifically, Equation of Motion Coupled Cluster (EOM-CC) is compared to the current state-of-the-art method, the so-called GW approximation for the GW100 test set. Ongoing challenges to the implementation of periodic EOM-CC including finite size effects, basis set effects, and pseudopotentials to reduce computational complexity will be addressed. Preliminary results indicate that this problem is not trivial and requires consideration of many inputs and extrapolation schemes in order to achieve reliable results. In addition to these computational schemes, a systematic hierarchy of approximations is introduced to quantitatively gauge computational cost and accuracy trade-offs, exploring theoretical errors in addition to computational errors. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S31.00004: Efficient Implementation of Exact Exchange for Periodic Systems within Concentric Atomic Density Fitting Approximation Xiao Wang, Cannada Lewis, Edward Valeev Development of electronic structure theory methods for periodic systems has been hampered for decades due to the unaffordable scaling with system size. One of the obstacles is the computation of two-electron repulsion integrals, whose near-field interaction can only be computed exactly or approximated using density fitting (DF). In this work, a massively-parallel implementation of an efficient local DF algorithm is presented in which atomic orbital (AO) products are fitted using only auxiliary AOs on one of the nuclei in that product. We applied this approach on the exact exchange term in Hartree-Fock with periodic boundary conditions (periodic HF) based on linear combinations of Gaussian-type AOs. Our algorithm has shown a significant reduction of computational costs with an accuracy below millihartree per atom, and thus will be beneficial to both hybrid density functional theory and post-HF methods. |
Thursday, March 7, 2019 12:27PM - 1:03PM |
S31.00005: The treatment of vacuum in semi-periodic post-HF methods Invited Speaker: Qiming Sun When a system has semi-periodic boundary condition, caution is needed to remove the interaction between the overall potential and the charge density in the neighboring boxes. For neutral systems, owing to the locality of one-body potential, a common trick in DFT calculations is to use a finite space of vacuum to mimic the free boundary. When moving to the periodic post-HF methods, the effectiveness of this treatment was yet verified. It was known that the finite-size correction to HF needs to be carefully handled in the periodic coupled cluster methods [1]. When the same treatment was applied to low-dimension systems, numerical uncertainty or slow convergence were observed. We compared the effects of vacuum treatments in periodic-MP2, periodic-CCSD calculations. We observed that the finite-size correction at HF level has different effects on different post-HF methods. In this talk, we will analyze the reasons that cause the numerical issues in semi-periodic post-HF methods. For different periodic post-HF methods, different solutions will be presented. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S31.00006: Optical properties of doped nanocrystals from correlated quantum chemistry Bryan Lau, Timothy Berkelbach Doped nanocrystals exhibit infrared absorption and are promising candidates for sensors, solar enegy conversion, and optical communications. The infrared absorption appears to undergo a transition from a single-particle to plasmonic absorption as a function of doping density and radius. This transition is not well understood from an experimental or theoretical point of view. This talk will present results from correlated quantum chemistry calculations of a particle-in-a-sphere model for a doped nanocrystal. The transition of the infrared absorption from single-particle to plasmonic is found to also depend on the absolute number of doped electrons. In particular, a single-particle transition can be broken into true single-particle, and Coulombically bound, but collective, excitations. These results highlight the importance of many-body exchange and correlation effects in quantum confined nanostructures. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S31.00007: Quasiparticle spectra of polyacetylene using coupled-cluster singles and doubles (CCSD) Taichi Kosugi, Yu-ichiro Matsushita Recently applications of CCSD method with Green's functions (GFs) to realistic systems are increasing rapidly.[1-3] |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S31.00008: Coupled cluster theory for condensed phase spectroscopy Alan Lewis, Timothy Berkelbach We use state-of-the-art equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD) to calculate the dynamic structure factor of the uniform electron gas. Our calculations are performed at densities corresponding to the valence electron densities of common metals. We compare our results to those obtained using the random-phase approximation, which is known to provide a reasonable description of the collective plasmon excitation. We find that EOM-CCSD, instead of providing a perturbative improvement on the RPA plasmon, predicts a many-state plasmon resonance, where each contributing state has a double-excitation character of 80 percent or more. This finding amounts to an ab initio treatment of the plasmon linewidth and highlights the strongly correlated nature of lifetime effects in condensed-phase electronic structure theory. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S31.00009: Effect of basis set on the outcome of external energy mediated chemical reactions Sharma SRKC Yamijala, zulfi ali, Bryan M Wong Directing the energies of an hot-electron or atom or molecule towards a specific vibrational mode to tune the reaction outcomes is an active area of catalytic research and ab initio molecular dynamics is one of the indispensable tools in understanding the mechanistic details of these reactions. In this work, we show that the predicted thermodynamic and catalytic properties of a reaction using an AIMD simulation highly depends on the quality of the employed basis set. To this end, we have considered the reactants and products of the water-gas shift reaction (viz., CO, CO2, H2, and H2O) and studied their interaction with the ZnO(10-10) surface using DFT and Born Oppenheimer Molecular Dynamics (BOMD) simulations. By merely changing the quality of the basis set from double zeta (commonly used in most calculations of these systems) to triple zeta, we show that the reaction outcome of an H2O molecule colliding with a ZnO surface pre-covered with carbon monoxide gives qualitatively different results. Furthermore, we show that the calculated adsorption energies can vary by as much as 380 meV (which is an order of magnitude larger than room temperature) by merely changing the basis. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S31.00010: Electronic Structure of NiO from Gaussian-based Periodic Coupled Cluster Theory Yang Gao, Mario Motta, James McClain, Qiming Sun, Garnet Chan, Austin Minnich Accurate description of ground and excited state properties of strongly correlated materials is a grand challenge in ab initio condensed matter simulation. While typical mean field methods performs poorly for these solids, increase in computational power now allows us to employs time-independent perturbation theory in quantum chemistry to systematically improve towards the exact solution for crystalline materials. Here, we present a numerical study of NiO using a Gaussian-based periodic coupled cluster method with single and double excitations. We compute ground-state properties of the antiferromagnetic phase as well as the quasiparticle band structure using the equation of motion ansatz (EOM-CCSD). We compare our results to other ab-initio methods and experimental data. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700