Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R02: Developments of DFT from Quantum to Statistical Mechanics (V)Focus
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Sponsoring Units: DCP DCOMP Chair: Thomas Miller, Caltech Room: LACC 150B |
Thursday, March 8, 2018 8:00AM - 8:36AM |
R02.00001: Finite temperature, classical DFT, and functionals from embedding Invited Speaker: Garnet Chan I will discuss a number of formal results in finite temperature and classical DFT. If time permits, I will also discuss quantum embedding theories from the viewpoint of functional construction. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R02.00002: Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional Georgia Prokopiou, Iulia Brumboiu, Leeor Kronik, Barbara Brena We analyze the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (α) included in the hybrid functional and the range-separation parameter (γ), with two strategies employed for finding the optimal γ for each α. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to literature gas-phase photo-electron data and GW calculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned γ, determined for the optimal value of α = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R02.00003: Asymptotic Analysis of Atomic Pauli Potentials Jeremy Redd, Antonio Cancio In orbital free (OF) DFT, the functional derivative of the Pauli contribution to the Kohn-Sham kinetic energy, the Pauli potential, is key to solving for the density. It can be expressed as the Pauli kinetic energy per particle, plus a response potential which describes the response of this quantity to a change in density. We have constructed the exact response and Pauli potentials for closed shell atoms for which the former becomes an exact eigenvalue expression, extended to large Z atoms attainable only in theory. We have done this non-relativistically because of the known asymptotic behavior of a semi-classical Fermi-electron gas, which is the limit of the core electrons of an atom as nuclear charge approaches infinity. In this limit and as radius approaches zero, we can show that the Pauli potential approaches the magnitude of the lowest energy eigenvalue. We have also compared several gradient expansions to test their utility as orbital free approximations to the response potential. This research may help produce orbital free approximations to the Pauli potential with proper Z scaling, and by extension may generate OFDFT models that can solve for the density of both homogeneous and inhomogeneous systems. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R02.00004: Nonlocal Kinetic Energy Functionals By Functional Integration Michele Pavanello Starting with the seminal works of Thomas and Fermi, the Density-Functional Theory (DFT) community has been searching for accurate electron density functionals. The typical paradigm is to first approximate the energy functional, and then take its functional derivative yielding a potential that can be used in DFT simulations. In this work, we take a different route and construct the potential from the second-functional derivative by functional integration. Following this principle, we prescribe two nonlocal noninteracting Kinetic Energy functionals, $T_{s}[\rho]$, having density dependent and independent kernels, respectively. The functionals satisfy three exact conditions: (1) the existence of a “kinetic electron” arising from the existence of the exchange hole; (2) for homogeneous densities, the second functional derivative is the inverse Lindhard function; (3) potential and energy derive by functional integration of the second derivative involving a line integral. In pilot calculations the functionals are capable of reproducing Kohn–Sham DFT equilibrium volumes, bulk moduli, phase energy ordering and electron densities for CD, FCC, and BT Silicon as well as FCC Aluminum. Although more benchmark work is needed, the results are very encouraging. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R02.00005: Nuclear quantum effect on hydrogen bond network fluctuation in liquid water inferred by X-ray absorption spectra Zhaoru Sun, Lixin Zheng, Mohan Chen, Francesco Paesani, Xifan Wu Based on state of the art path-integral molecular dynamics simulations carried out with the MB-pol water model and calculations of electronic excitations within the self-consistent GW theory, we investigate nuclear quantum effects (NQEs) on the oxygen K-edge X-ray absorption spectra (XAS) of water at various temperatures. Under the influence of NQEs, protons are more delocalized, which significantly broadens the calculated XAS spectra. Furthermore, NQEs are responsible for nontrivial competing effects on the hydrogen bond network. On one hand, the liquid structure is slightly softened due to the presence of more broken hydrogen bonds. On the other hand, configurations with stronger hydrogen bonds are largely favored by proton delocalization. These competing NQEs yield important corrections on the calculated XAS spectra as demonstrated by red (blue) shifts of the main-edge (post-edge). The calculated XAS spectra are in nearly quantitative agreement with the available experimental data. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R02.00006: Constructing fragment-density functionals Kaili Jiang, Jonathan Nafziger, Adam Wasserman Approximations of the non-additive non-interacting kinetic energy (NAKE) as an explicit functional of the density are the basis of fragment-based methods that provide improved computational efficiency over standard Kohn-Sham calculations. However, within most fragment-based formalisms, there is no unique NAKE, making it difficult to develop general, robust approximations to it. In Partition Density Functional Theory, the ambiguity of the NAKE is removed and approximate functionals may be more meaningfully compared to exact quantities. We discuss promising avenues for constructing fragment density-functionals for the NAKE: (1) By re-parametrizing decomposable conjoint functionals for weakly-bonded systems; (2) By designing non-decomposable functionals for weak and covalent bonds that satisfy exact constraints of the partition energy without fitting. |
Thursday, March 8, 2018 9:36AM - 10:12AM |
R02.00007: DFT beyond the ground-state: memory-dependent functionals and coupling to ions Invited Speaker: Neepa Maitra The adiabatic approximations currently used in time-dependent density functionals describe exchange-correlation effects that depend only on the instantaneous density. However, recent work has shown that dependence on the history of the density and initial states is important to incorporate for accurate simulations of the dynamics, especially for systems driven far from the ground-state. In many applications when strong lasers are involved, the electron and nuclear dynamics happen on a similar time-scale, especially when light nuclei are present, and the effects of correlation between the electron dynamics and quantum ion dynamics can be significant. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R02.00008: Exact and Approximate Ensemble Density Functionals for a Simple model Francisca Sagredo, Kieron Burke Ensemble density functional theory (eDFT) has been of recent interest since it provides an alternative to the traditional time-dependent density functional theory (TD-DFT). Although TD-DFT has many benefits, and is thus considered the standard method for solving for excited states, it still has many difficulties that are vital for understanding chemical processes. Such difficulties include: not being able to solve for multiple excitations, long range charge transfers, and conical intersections, thus making eDFT a useful alternative method to investigate. We have chosen the Hubbard dimer as the simple system to study where eDFT. This model is truncated to be a two site, dimer making all of the solutions analytic, and therefore a “toy-like” model where we can control the correlation and the potential between the two sites. After derivation of simple functionals, the symmetry eigenstate hartree exchange approximation (SEHX) was tested for this model system. Using the SEHX approximation the first excited singlet state has been extracted for the dimer, as well as for the doubly occupied second excited state, which is a double excitation. Charge transfer excitations are also investigated. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R02.00009: ABSTRACT WITHDRAWN
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Thursday, March 8, 2018 10:36AM - 10:48AM |
R02.00010: A unified treatment of derivative discontinuity, delocalization and static correlation effects in DFT: the LDA plus Density Matrix Minimization (LDA+DMM) method Fei Zhou, Vidvuds Ozolins
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Thursday, March 8, 2018 10:48AM - 11:00AM |
R02.00011: CAP-DD: Improved Correct Asymptotic Potential GGA with Derivative Discontinuity Treatment Sam Trickey, Javier Carmona-Espindola, Jose Gazquez, Alberto Vela We summarize development and performance of a much-improved non-empirical, constraint-based generalized gradient approximation (GGA) exchange functional which has exchange potentials with correct asymptotic behavior (-1/r). It advances over our original “CAP” [J. Chem. Phys. 142, 054105 (2015)] via derivative discontinuity treatment and removal of a spurious mid-range bump in the exchange potential. The mid- and long-range behavior improvements follow from analysis of all sources of pure (-1/r) asymptotic behavior and constraint-based combination of them. Derivative discontinuity is treated by internally consistent treatment of potential shift and approximate self-interaction correction follows from exact calibration to the H atom. Calculated results for standard molecular tests (heats of formation, ionization potentials, electron affinities, bond lengths, barrier heights, etc.) as well as polarizabilities, hyperpolarizabilities, and treatment of excited states, show that the new CAP-DD in many cases is superior to popular GGA functionals, always is competitive, and is competitive with such semi-empirical hybrids as B3LYP. |
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