Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L1: Recent Advances in Density Functional Theory V |
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Sponsoring Units: DCP DCOMP Chair: Aurora Pribram-Jones, University of California, Irvine Room: 103/105 |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L1.00001: Recent progress in density functional theory Invited Speaker: Donald Truhlar Ongoing work involves several areas of density functional theory: new methods for computing electronic excitation energies, including a new way to remove spin contamination in the spin-flip Tamm-Dancoff approximation and a configuration-interaction-corrected Tamm-Dancoff Approximation for treating conical intersections; new ways to treat open-shell states, including a reinterpreted broken-symmetry method and multi-configuration Kohn-Sham theory; a new exchange-correlation functional; new tests of density functional theory against databases for electronic transition energies and molecules and solids containing metal atoms; and applications. A selection of results will be presented. I am grateful to the following collaborators for contributions to the ongoing work: Boris Averkiev, Rebecca Carlson, Laura Fernandez, Laura Gagliardi, Chad Hoyer, Francesc Illas, Miho Isegawa, Shaohong Li, Giovanni Li Manni, Sijie Luo, Dongxia Ma, Remi Maurice, Rub\'{e}n Means-Pa\~{n}eda, Roberto Peverati, Nora Planas, Prasenjit Seal, Pragya Verma, Bo Wang, Xuefei Xu, Ke R. Yang, Haoyu Yu, Wenjing Zhang, and Jingjing Zheng. [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L1.00002: Density-Decomposed Orbital-Free Density Functional Theory for Covalent Systems and Application to Li-Si alloys Junchao Xia, Emily Carter We propose a density decomposition scheme using a Wang-Govind-Carter (WGC)-based kinetic energy density functional (KEDF) to accurately and efficiently simulate covalent systems within orbital-free (OF) density functional theory (DFT). By using a local, density-dependent scale function, the total density is decomposed into a localized density within covalent bond regions and a flattened delocalized density, with the former described by semilocal KEDFs and the latter treated by the WGC KEDF. The new model predicts reasonable equilibrium volumes, bulk moduli, and phase ordering energies for various semiconductors compared to Kohn-Sham (KS) DFT benchmarks. The surface energy of Si(100) also agrees well with KSDFT. We further apply the model to study mechanical properties of Li-Si alloys, which have been recently recognized as a promising candidate for next-generation anodes of Li-ion batteries with outstanding capacity. We study multiple crystalline Li-Si alloys. The WGCD KEDF predicts accurate cell lattice vectors, equilibrium volumes, elastic moduli, electron densities, alloy formation and Li adsorption energies. Because of its quasilinear scaling, coupled with the level of accuracy shown here, OFDFT appears quite promising for large-scale simulation of such materials phenomena. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L1.00003: Density-Functional Theory of Thermal Transport F.G. Eich, A. Principi, M. Di Ventra, G. Vignale We have recently introduced a non-equilibrium density-functional theory of local temperature and associated energy density that is suitable for the study of thermoelectric phenomena from first principles [1]. This theory rests on a local temperature field coupled to the energy-density operator. Here we apply the theory to a simple two-terminal setup, in which the terminals are held at different temperatures. We show that our treatment becomes equivalent to the standard Landauer-B{\"u}ttiker formulation of thermal transport in the non-interacting limit. \\[4pt] [1] arXiv:1308.2311 [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L1.00004: Accurate and systematically improvable quantum embedding methods for complex systems Jason Goodpaster, Taylor Barnes, Frederick Manby, Thomas Miller We describe embedded density functional theory (e-DFT) methods that avoid approximations to the kinetic energy functional and provide a formally exact approach to performing electronic structure calculations in the e-DFT framework. This framework allows systems to be divided into smaller subsystems which can be treated at different levels of theory, with the intersubsystem potential calculated using our e-DFT protocol. We use this framework to develop robust wavefunction embedding methods. This allows for wavefunction calculations to be used in regions of large systems where DFT is known to perform poorly, such as van der Waals interactions and strongly correlated electrons. Through a systematic analysis of embedding errors, we determine the largest source of error from wavefunction-in-DFT embedding to be the evaluation of the approximate non-additive exchange-correlation functional. We suggest new algorithms to systematically reduce these errors. These improvements allow for embedding methods that accurately reproduce reference couple-cluster calculations for a series of chemical reactions. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:48AM |
L1.00005: Wavefunctions, Adiabatic Connections, and Universal Functionals for 1-Matrix Functional Theory Invited Speaker: Paul Ayers In Kohn-Sham density functional theory, a reference system of noninteracting electrons with the same density as the physical system is used as a zeroth-order approximation to the system. Using an adiabatic connection to the target system, one can then correct the Kohn-Sham approximation. In this talk, I will establish an analogous approach for the 1-electron reduced density matrix (DM1). The reference system now contains \textit{interacting} electrons, which we choose to describe with the Richardson Hamiltonian. The Richardson Hamiltonian includes the noninteracting-electrons limit (Kohn-Sham) and strictly-correlated-electrons limit (antisymmetrized geminal power). Any singlet-state DM1 can be reproduced by a Richardson Hamiltonian, and an adiabatic connection from the Richardson Hamiltonian to the target physical system provides a rigorous definition for the correlation functional in 1-density matrix functional theory (DM1FT). Preliminary numerical results are favorable. Because DM1FT treats both the strongly correlated and weakly correlated limits exactly, it seems to be a very promising avenue for research. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L1.00006: Semiclassical approach to the exchange energy from potential functional theory Attila Cangi, Peter Elliott, Stefano Pittalis, E.K.U. Gross, Kieron Burke Although Kohn-Sham (KS) density functional theory is being successfully and ever increasingly applied for computing the electronic structure of matter, there is a lack of a systematic procedure for deriving reliable approximations for its main ingredient -- the exchange-correlation (XC) energy functional. Potential functional theory[1,2,3] is an alternative approach that may provide a solution to this long-standing problem. In our line of research we had only considered potential functional approximations to the KS kinetic energy[4,5] so far. In this work, we (i) propose approximating the XC energy straight as a functional of the KS potential and (ii) derive a highly accurate potential functional approximation to the exchange energy for the simplest relevant model system using semiclassical techniques[6]. [1] W. Yang, P. W. Ayers, and Q. Wu, Phys. Rev. Lett. 92, 146404 (2004). [2] A. Cangi, D. Lee, P. Elliott, K. Burke, and E.K.U. Gross, Phys. Rev. Lett. 106, 236404 (2011). [3] A. Cangi, E.K.U. Gross, K. Burke, Phys. Rev. A (2013), accepted. [4] P. Elliott, D. Lee, A. Cangi, and K. Burke, Phys. Rev. Lett. 100, 256406 (2008). [5] A. Cangi, D. Lee, P. Elliott, and K. Burke, Phys. Rev. B 81, 235128 (2010). [6] A. Cangi, P. Elliott, S. Pittalis, E.K.U. Gross, K. Burke, submitted. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L1.00007: Three- to two-dimensional crossover in time-dependent density-functional theory Shahrzad Karimi, Carsten Ullrich Quasi-two-dimensional (2D) systems, such as an electron gas confined in a quantum well, are of great theoretical interest and practical importance. Earlier studies of the crossover from 3D to 2D in ground-state density-functional theory have shown that local and semilocal exchange-correlation functionals which are based on the 3D electron gas as reference system work well for wide quantum wells, but eventually break down as the true 2D limit is approached. We now consider the dynamical case and study the performance of various linear-response exchange kernels in time-dependent density-functional theory. We compare approximate local and orbital-dependent exchange kernels with time-dependent Hartree-Fock theory for n-doped quantum wells, and analyze their behavior for intersubband charge and spin plasmons as they cross over from the quasi-2D to the bulk plasmon regime. [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L1.00008: Stationary state Kohn-Sham Theory: Modern algorithms breathe new life into an old theory Deniz Gunceler, Ravishankar Sundararaman, T.A. Arias In this talk, we will discuss stationary-state Kohn-Sham theory, an old (Phys. Rev. B 31, 6264-6272) but largely ignored idea that is recently undergoing revival. It is based on an in-principle exact scheme in which excited states are computed as the stationary states of the Hohenberg-Kohn functional. We will discuss the objections of Gaudoin and Burke (Phys. Rev. Lett. 93, 17), and also describe the computational difficulties which prevented this theory from becoming popular in the past, and present new algorithms for computing the predictions of this theory. The resulting technique has inherent computational advantages over TDDFT and GW, and results using semilocal functionals show great promise for molecules. However, the method as implemented exhibits large errors for solids. In this talk, we shall show that the origin of this behaviour is related to the fact that different errors dominate the solid and molecular cases, and we shall discuss prospects for improvement of the theory in the future. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L1.00009: Increasing the efficiency and accuracy of time-resolved electronic spectra calculations with on-the-fly ab initio quantum dynamics methods Jiri Vanicek Rigorous quantum-mechanical calculations of coherent ultrafast electronic spectra remain difficult. I will present several approaches developed in our group that increase the efficiency and accuracy of such calculations: First, we justified the feasibility of evaluating time-resolved spectra of large systems by proving that the number of trajectories needed for convergence of the semiclassical dephasing representation/phase averaging is independent of dimensionality. Recently, we further accelerated this approximation with a cellular scheme employing inverse Weierstrass transform and optimal scaling of the cell size. The accuracy of potential energy surfaces was increased by combining the dephasing representation with accurate on-the-fly ab initio electronic structure calculations, including nonadiabatic and spin-orbit couplings. Finally, the inherent semiclassical approximation was removed in the exact quantum Gaussian dephasing representation, in which semiclassical trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. Among other examples I will present an on-the-fly ab initio semiclassical dynamics calculation of the dispersed time-resolved stimulated emission spectrum of the 54-dimensional azulene. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L1.00010: Exploring Nuclear Effects in the Dynamics of Nanomaterials with a Quantum Trajectory-Electronic Structure Approach Sophya Garashchuk A massively parallel, direct quantum molecular dynamics method is described. The method combines a quantum trajectory (QT) representation of the nuclear wavefunction discretized into an ensemble of trajectories with an electronic structure (ES) description of electrons, namely using the Density Functional Tight Binding (DFTB) theory. Quantum nuclear effects are included into the dynamics of the nuclei via quantum corrections to the classical forces. To reduce computational cost and increase numerical accuracy, the quantum corrections to dynamics resulting from localization of the nuclear wavefunction are computed approximately and included into selected degrees of freedom representing light particles where the quantum effects are expected to be the most pronounced. A massively parallel implementation, based on the Message Passing Interface allows for efficient simulations of ensembles of thousands of trajectories at once. The QTES-DFTB dynamics approach is employed to study the role of quantum nuclear effects on the interaction of hydrogen with a model graphene sheet, revealing that neglect of nuclear effects can lead to an overestimation of adsorption. [Preview Abstract] |
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