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

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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 abinitio 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 activespace selfconsistent field method: a sizeextensive, linearscaling MCSCF approach for stronglycorrelated 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 stronglycorrelated 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 costcontrolling approximations such as restricted or generalized active space (RAS, GAS) do not resolve this difficulty. However, our recentlydeveloped localized active space (LAS) SCF method, which is based on a union of density matrix embedding theory (DMET) and MCSCF concepts, generates a wave function which, unlike RAS or GAS, is multiplicatively separable between disjoint, realspacelocalized 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 stronglycorrelated systems and show that LASSCF gives CASSCFquality results, implying an attractive possibility for computing wave functions of stronglycorrelated condensed systems. 
Thursday, March 7, 2019 12:03PM  12:15PM 
S31.00003: Transitioning HighAccuracy 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 (EOMCC) is compared to the current stateoftheart method, the socalled GW approximation for the GW100 test set. Ongoing challenges to the implementation of periodic EOMCC 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 tradeoffs, 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 twoelectron repulsion integrals, whose nearfield interaction can only be computed exactly or approximated using density fitting (DF). In this work, a massivelyparallel 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 HartreeFock with periodic boundary conditions (periodic HF) based on linear combinations of Gaussiantype 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 postHF methods. 
Thursday, March 7, 2019 12:27PM  1:03PM 
S31.00005: The treatment of vacuum in semiperiodic postHF methods Invited Speaker: Qiming Sun When a system has semiperiodic 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 onebody 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 postHF methods, the effectiveness of this treatment was yet verified. It was known that the finitesize correction to HF needs to be carefully handled in the periodic coupled cluster methods [1]. When the same treatment was applied to lowdimension systems, numerical uncertainty or slow convergence were observed. We compared the effects of vacuum treatments in periodicMP2, periodicCCSD calculations. We observed that the finitesize correction at HF level has different effects on different postHF methods. In this talk, we will analyze the reasons that cause the numerical issues in semiperiodic postHF methods. For different periodic postHF 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 singleparticle 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 particleinasphere model for a doped nanocrystal. The transition of the infrared absorption from singleparticle to plasmonic is found to also depend on the absolute number of doped electrons. In particular, a singleparticle transition can be broken into true singleparticle, and Coulombically bound, but collective, excitations. These results highlight the importance of manybody exchange and correlation effects in quantum confined nanostructures. 
Thursday, March 7, 2019 1:15PM  1:27PM 
S31.00007: Quasiparticle spectra of polyacetylene using coupledcluster singles and doubles (CCSD) Taichi Kosugi, Yuichiro Matsushita Recently applications of CCSD method with Green's functions (GFs) to realistic systems are increasing rapidly.[13] 
Thursday, March 7, 2019 1:27PM  1:39PM 
S31.00008: Coupled cluster theory for condensed phase spectroscopy Alan Lewis, Timothy Berkelbach We use stateoftheart equationofmotion coupledcluster theory with single and double excitations (EOMCCSD) 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 randomphase approximation, which is known to provide a reasonable description of the collective plasmon excitation. We find that EOMCCSD, instead of providing a perturbative improvement on the RPA plasmon, predicts a manystate plasmon resonance, where each contributing state has a doubleexcitation 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 condensedphase 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 hotelectron 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 watergas shift reaction (viz., CO, CO2, H2, and H2O) and studied their interaction with the ZnO(1010) 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 precovered 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 Gaussianbased 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 timeindependent 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 Gaussianbased periodic coupled cluster method with single and double excitations. We compute groundstate properties of the antiferromagnetic phase as well as the quasiparticle band structure using the equation of motion ansatz (EOMCCSD). We compare our results to other abinitio methods and experimental data. 
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