Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P02: Developments of DFT from Quantum to Statistical Mechanics (IV)Focus

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Sponsoring Units: DCP DCOMP Chair: Tomas Arias, Cornell University Room: LACC 150B 
Wednesday, March 7, 2018 2:30PM  3:06PM 
P02.00001: Efficient molecular density functional theory using generalized spherical harmonics expansions Invited Speaker: Maximilien Levesque , Lu Ding , Luc Belloni , Daniel Borgis We show that generalized spherical harmonics are well suited a basis set for representing the space and orientation molecular density for the resolution of the (classical) molecular density functional theory. We consider the common system made of a rigid molecule of arbitrary complexity immersed in a molecular solvent, both represented by molecules with interacting atomic sites and classical force fields. The molecular solvent density ρ(r,Ω) around the solute is a function of the position r and of the three Euler angles Ω describing the solvent orientation. The standard density functional, equivalent to the HNC closure for the solutesolvent correlations in the liquid theory, is minimized with respect to ρ(r,Ω). The uptonow very expensive angular convolution products are advantageously replaced by simple products between projections onto generalized spherical harmonics. The dramatic gain in speed of resolution enables to explore in a systematic way molecular solutes of up to nanometric sizes in arbitrary solvents and to calculate their solvation free energy and associated microscopic solvent structure in at most a few minutes. We show how this theory must be completed to fulfil thermodynamic consistency, at least in terms of pressure and surface tension. We finaly illustrate the formalism by tackling the solvation of molecules of various complexity in water. 

P02.00002: ABSTRACT WITHDRAWN

Wednesday, March 7, 2018 3:18PM  3:30PM 
P02.00003: Connecting Quantum and Classical DFT Dennis Perchak , Kieron Burke Because particles are distinguishable in classical DFT, one can relate the pair correlation function of a uniform system to the density response of an inhomogeneous system, in which one of the particles is considered an external impurity. We apply the same reasoning as an uncontrolled approximation to estimate the pair correlation function of a uniform quantum electron gas, assuming one of the electrons can be distinguished from all others (a ``blue" electron). The errors in this approximation should shrink with increasing temperature. We report the accuracy and limitations of this approach. 
Wednesday, March 7, 2018 3:30PM  3:42PM 
P02.00004: Steps in the Exact KohnSham Potential of Ensemble Densityfunctional Theory for Excited States and Their Relation to the Derivative Discontinuity Matt Hodgson , Eli Kraisler , Mike Entwistle , Axel Schild , Eberhard K Gross An accurate approximation to the exchangecorrelation (xc) part of the KohnSham (KS) potential is essential for any densityfunctional calculation. Densityfunctional theory (DFT) is widely used in condensed matter physics, quantum chemistry and many other fields. Therefore, understanding the behaviour of the exact xc potential and developing improved approximations to it are of the utmost importance. The focus of calculations within DFT is usually on the ground state. However, knowledge of how the system responds to an excitation is important. In this talk we present the exact KS potential of an ensemble of the ground state and the first excited state of a 1D diatomic molecule. For this system, upon excitation, a small amount of charge transfers from one atom to the other. In the corresponding exact ensemble xc potential we find two plateaus: one that forms around the nucleus of the acceptor atom, associated with the derivative discontinuity of that atom (Δ), and another that forms around the donor atom and corresponds to a new phenomenon which we term the 'chargetransfer derivative discontinuity'. The relevance of the aforementioned features to an accurate prediction of the excitation spectrum is discussed. 
Wednesday, March 7, 2018 3:42PM  3:54PM 
P02.00005: TimeDependent MultiComponent Density Functional Theory for Coupled ElectronPositronNuclear Dynamics Yasumitsu Suzuki , Satoshi Hagiwara , Kazuyuki Watanabe Positrons have been studied and utilized in various fields of molecular physics and surface science. We are particularly interested in dynamics of positronatom compound systems under laser fields, which has been actively conducted mainly by experiments, because the microscopic mechanism of correlated dynamics of positrons with electrons and nuclei in these experiments is far from understanding. Here we propose and develop timedependent multicomponent density functional theory (TDMCDFT) for coupled electronpositron dynamics to explore the dynamics of positronmolecular compound systems. This TDMCDFT is a firstprinciples approach that can simulate formally exact excited state quantum dynamics of coupled electronpositron systems. In the present work we propose an adiabatic local density approximation for timedependent electronpositron correlation. We apply this TDMCDFT approach to the dynamics of positron detachment from polar and nonpolar molecules under various laser fields. Furthermore we derive the TDMCDFTEhrenfest molecular dynamics scheme to account for the coupling to nuclear motion. We elucidate the difference in the dynamics between polar and nonpolar molecules and how laser intensity and frequency and nuclear motion play a role for efficient positron detachment. 
Wednesday, March 7, 2018 3:54PM  4:06PM 
P02.00006: Validating Molecular Dynamics and Joint DFT Predictions of Interfacial Water Using XRay Reflectivity Kendra LetchworthWeaver , Katherine Harmon , Alex Gaiduk , Federico Gilberti , Francois Gygi , Maria Chan , Giulia Galli , Paul Fenter Capturing the structure and properties of water next to a solid surface presents a unique challenge for both KohnSham and classical densityfunctional theories due to a complex interplay between chemical binding, electrostatic interactions, steric effects, and dispersion. Xray reflectivity measurements determine the electron density of aqueous interfaces with high precision, but rely on modeldependent fitting to obtain the corresponding structural model. We present a validation protocol which enables calculation of interfacial Xray structure factors from theory for direct comparison to experimental measurements. We apply this protocol to benchmark first principles molecular dynamics, classical molecular dynamics, and joint DFT simulations of the Al_{2}O_{3}/water interface, probing the effect of pressure, temperature, and finite size upon the predicted structural model. We explore the relative strengths and weaknesses of each class of theory, gaining insights into the bonding and structural properties of interfacial water which will aid future development of more accurate electronic and classical densityfunctionals. 
Wednesday, March 7, 2018 4:06PM  4:42PM 
P02.00007: DFTbased embedding theories: Wavefunctionembedding, dynamics, excited states, and applications Invited Speaker: Thomas Miller The simulation of chemical dynamics in complex systems demands the development of methods with improved accuracy and computational scaling. Density functional theory (DFT) provides a rigorous and flexible framework for achieving this aim, by enabling the embedding of either (i) a subsystem described at the accurate wavefunction level in a DFT environment or (ii) a subsystem described at the DFT level in a tightbinding environment. My talk will focus on recent developments along these lines, including the use of such methods to describe ground and excitedstate chemical dynamics and surface reactions in condensedphase systems. 
Wednesday, March 7, 2018 4:42PM  4:54PM 
P02.00008: Applying Exact Conditions to Machine Learned Density Functionals Jacob Hollingsworth , Li Li , Kieron Burke Historical methods of functional development in density functional theory have been largely guided by analytic conditions that constrain the exact functional one is trying to approximate. Recently, machine learning functionals, which are formed by extrapolating the results from a small number of exactly solved systems to unsolved systems that are similar in nature, have turned away from utilizing constraints on the exact functional. In this work, we show that imposing these exact conditions onto machine learning functionals can improve the ability of the machine learning functionals to extrapolate to unsolved systems. 
Wednesday, March 7, 2018 4:54PM  5:06PM 
P02.00009: Generating Generalized Kpoint Grids on the fly Wiley Morgan , Parker Hamilton , John Christensen , Rod Forcade , Gus Hart Traditionally, Brillouin zone integration has been done using MonkhorstPack Kpoint grids. Recently, Wisesa et. al. [1] were able to build a database of more general grids that have better folding than traditional MonkhorstPack grids. The better folding allows for increased performance in Density Functional Codes. Leveraging concepts from group theory we have developed an ontheflyalgorithm that generates general Kpoint grids that have optimal Kpoint folding. 
Wednesday, March 7, 2018 5:06PM  5:18PM 
P02.00010: Inclusion of the ionic zeropoint motion in the density functional theorybeyond the BornOppenheimer approximation Efstratios Manousakis , Grigory Kolesov , Efthimios Kaxiras We introduce a novel method to carry out a zero temperature density functional theory (DFT) calculation for systems in which the ionic motion is treated fully quantum mechanically and the electronic degrees of freedom are treated within imaginarytime dependent DFT. The approach is based on the finitetemperature manybody pathintegral formulation of quantum mechanics by taking the zerotemperature limit and treating the imaginarytime propagation of the electronic variables ``exactly'' within the DFT. Our approach goes beyond the familiar BornOppenheimer approximation and is limited from being exact only by the approximations involved in the DFT approach and it includes the effects of the electronic charge correlations in imaginary time. The method is tested in simple molecules which contain light atoms, such as hydrogen, where the fluctuations of the distance from its equilibrium position, due to the zeropointmotion, is comparable to the interatomic distances. 
Wednesday, March 7, 2018 5:18PM  5:30PM 
P02.00011: Utilizing Advanced Kinetic Energy Density Based Ingredients for Novel Local Hybrid Mixing Functions James Furness , Jianwei Sun Density functional theory (DFT) has become an invaluable tool across many domains of chemistry and materials science, a success made possible by the high accuracy and efficiency of modern density functional approximations (DFA). Despite continued progress in functional design, conventional DFAs suffer a poor description of the strong manyelectron interaction (SMEI) and selfinteraction error (SIE). Such deficiencies degrade accuracy in predictions of many properties important for energy applications, including band gaps, stretched bonds, catalysis, charge transfer processes, and reaction barriers^{1}. 
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