Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B24: Electronic Structure Methods I |
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Sponsoring Units: DCOMP Chair: Mark Pederson, United States Department of Energy Room: 203AB |
Monday, March 2, 2015 11:15AM - 11:27AM |
B24.00001: Electron localization in exact time-dependent density-functional potentials Matthew Hodgson, James Ramsden, Thomas Durrant, Jacob Chapman, Piers Lillystone, Rex Godby By propagation of the exact many-electron wavefunction, we determine exact Kohn-Sham (KS) potentials for 1D systems with strong correlation [1]. From this we have developed a density functional which incorporates several features, present in the exact KS potential, that are entirely missing from the usual approximations made in time-dependent density-functional theory (TDDFT) [2]. We find a strong and time-dependent self-interaction correction, owing to electron localization, as well as large static and dynamic spatial steps in the KS potential. Our new functional, suited to simulating ground-state and time-dependent electronic systems, combines an expression for the exact KS potential in the limit of complete electron localization with a measure of the actual localization. Self-consistent application of the functional provides accurate densities for a range of systems, even where the KS potential requires non-local dependence on the charge density, such as potential steps; the self-interaction correction is accurately described. We explore the relationship between features in the KS potential and the ``derivative discontinuity.'' \\[4pt] [1] M. J. P. Hodgson \textit{et al.} \textbf{Phys. Rev. B} 88, 241102(R)\\[0pt] [2] M. J. P. Hodgson \textit{et al.} \textbf{arXiv:1409.5666} [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B24.00002: Constructing Multi-Slater-Jastrow Wavefunctions via Reduced Density Matrix Covariance Kiel Williams, Lucas Wagner The multi-determinant Slater-Jastrow ansatz wavefunction is a powerful tool for conducting ab initio electronic structure calculations in strongly correlated systems. We illustrate a new method of systematically constructing multi-determinant expansions by analyzing the covariance of elements of the two-body reduced density matrix (2RDM) with respect to the local energy distribution for a Slater-Jastrow wave function. By ordering the elements of the 2RDM with respect to their computed mean and associating each matrix element with a new determinant, we construct new multi-determinant expansions. We show that the energies of an H2 and stretched N2 molecule converge more rapidly with respect to the number of included determinants using this technique than in conventional configuration interaction calculations. This suggests that our analysis of the 2RDM captures qualitative differences between the single Slater determinant and the Slater-Jastrow wave function. This method provides a new way of diagnosing and correcting the deficiencies of certain trial wavefunction types in quantum Monte Carlo calculations. This work was supported by NSF DMR 12-06242. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B24.00003: Unitarily Invariant Self-Interaction Corrections to the Uniform Electron Gas Mark Pederson, Jianwei Sun A new formulation of the self-interaction correction (SIC) to density functional theory (DFT) based upon symmetrically orthogonalized ``Fermi-L{\"o}wdin orbitals'' (FLO) is reviewed [1]. This method leads to an energy that is explicitly unitarily invariant and size extensive and allows for implementation of SIC with the same efficient scaling offered by DFT. Initial applications to small molecules [1] provided orbitals that are similar to past results but yielded SIC-LDA cohesive energies that are competitive with GGA results. Investigations on a uniform electron gas (UEG) provide an additional challenging limit to consider. Results from FLO-based SIC calculations on the UEG, enclosed in a finite box, are presented. In accord with Ref. [2], the FLO-based formulation of SIC finds that localized Wannier orbitals lead to lower energies than plane waves in the exchange-only limit We compare total energies of the uniform electron gas, calculated within DFT, FLO-SIC-DFT, and HF, as a function of functional (including MGGAs[3]), electron number, volume, and Fermi-surface shape.\\[4pt] [1] M.R. Pederson, A. Ruzsinszky \& J.P. Perdew, JCP {\bf 140}, 121103 (2014).\\[0pt] [2] M.R. Pederson, R.A. Heaton, and J.G. Harrison, PRB {\bf 39}, 1581 (1989).\\[0pt] [3] J. Sun, A. Ruzsinszky \& J.P. Perdew (this meeting). [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B24.00004: Using Dielectric Properties to Design Nonempirical Hybrid Functionals for Accurate Electronic Structure Jonathan Skone, Marco Govoni, Giulia Galli Building upon a recently proposed self-consistent hybrid (sc-hybrid) functional [1], where the optimal dielectric screening is included self-consistently, we propose an improved form by incorporating range-separation of the exchange part. We discuss the choice of the non-empirical parameters defining range separation, and we present results for condensed media including semiconductors, amorphous insulators, and molecular crystals. We find that the range-separated sc-hybrid functional further improves upon the electronic gaps obtained with full-range sc-hybrids, thus providing an accurate functional for high throughput band gap engineering.\\[4pt] [1] Skone, Govoni, and Galli PRB 89 195112 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B24.00005: Range optimized theory of electron liquids with application to jellium James Donley, Craig Pryor A simple optimization scheme is used to compute the density-density response function of the 3-D homogeneous electron gas at zero temperature. Higher order terms in the perturbation expansion beyond the random phase approximation are summed approximately by enforcing the constraint that the spin density radial distribution functions be positive. Quantitative comparison is made with previous theory and data from quantum Monte Carlo simulation. Agreement with the available simulation data is good for the entire paramagnetic region. Generalization of the theory to inhomogeneous electron liquids such as in semiconductors will be discussed. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B24.00006: Inaccurate prediction of metal properties by hybrid functionals Weiwei Gao, Tesfaye Abtew, Peihong Zhang Although computationally demanding, hybrid functionals have been widely used in electronic structure calculations and have demonstrated certain advantages in predicting the band gap of semiconductors and insulators. The applications of hybrid functionals to metals, however, results in several serious issues. In this talk, we will discuss the applicability and limitations of hybrid functionals when it comes to predicting several important properties of metals such as electron-phonon coupling, lattice stability, and magnetism. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B24.00007: Density matrix perturbation theory for magneto-optical response of periodic insulators Irina Lebedeva, Ilya Tokatly, Angel Rubio Density matrix perturbation theory offers an ideal theoretical framework for the description of response of solids to arbitrary electromagnetic fields. In particular, it allows to consider perturbations introduced by uniform electric and magnetic fields under periodic boundary conditions, though the corresponding potentials break the translational invariance of the Hamiltonian. We have implemented the density matrix perturbation theory in the open-source Octopus code on the basis of the efficient Sternheimer approach. The procedures for responses of different order to electromagnetic fields, including electric polarizability, orbital magnetic susceptibility and magneto-optical response, have been developed and tested by comparison with the results for finite systems and for wavefunction-based perturbation theory, which is already available in the code. Additional analysis of the orbital magneto-optical response is performed on the basis of analytical models. Symmetry limitations to observation of the magneto-optical response are discussed. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B24.00008: Theoretical and experimental electronic structure of quinacridone Sivan Refaely-Abramson, Daniel Lueftner, Michael Pachler, Roland Resel, Michael G. Ramsey, Leeor Kronik, Peter Puschnig Although density functional theory is often used to study the frontier energy levels of organic electronic materials, standard functionals tend to predict too small fundamental gaps, may lead to wrong orbital energy ordering, and do not capture polarization-induced gap renormalization. We examine a strategy for overcoming these issues by studying the gas phase and bulk electronic structure of the organic molecule quinacridone, a promising material for organic devices. We employ the recently developed optimally tuned screened range-separated hybrid (OT-SRSH) functional [PRB 88, 081204(R) (2013)], where the electronic screening is taken into account, and compare with angle-resolved photoemission spectroscopy on multi-layers of quinacridone. Our method leads to the desired band gap renormalization and results in a valence band spectrum in excellent agreement with experimental data and with full-frequency G0W0 results based on a hybrid functional starting point. [PRB 90, 075204 (2014)] [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B24.00009: Helmholtz Fermi surface harmonics: an efficient approach for treating anisotropic problems involving Fermi surface integrals Asier Eiguren, Idoia G. Gurtubay We present a new efficient numerical approach for representing an-isotropic physical quantities and/or matrix elements defined on the Fermi surface (FS) of metallic materials. The method introduces a set of numerically calculated generalized orthonormal functions, which are the solutions of the Helmholtz equation defined on the FS, where the periodicity of the reciprocal space is treated as a boundary condition. In essence, what we introduce is a generalization of the Spherical Harmonics for any periodic Fermi Surface and regardless of its topology. The main motivation of the approach is to handle an-isotropic many-body problems very efficiently. In this context we demonstrate how our theory reduces, by several orders of magnitude, the computational effort when applied to several well know many-body theoretical models such as the electron-phonon. Moreover, the method is demonstrated to be very robust in handling problems with any crystal structure or topology of the FS. We illustrate the method showing applications on several relevant surface and bulk systems. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B24.00010: Efficient mixing scheme for self-consistent all-electron charge density Tatsuya Shishidou, Michael Weinert In standard {\it ab initio} density-functional theory calculations, the charge density $\rho$ is gradually updated using the ``input'' and ``output'' densities of the current and previous iteration steps. To accelerate the convergence, Pulay mixing has been widely used with great success. It expresses an ``optimal'' input density $\rho^{\mathrm{opt}}$ and its ``residual'' $R^{\mathrm{opt}}$ by a linear combination of the densities of the iteration sequences. In large-scale metallic systems, however, the long range nature of Coulomb interaction often causes the ``charge sloshing'' phenomenon and significantly impacts the convergence. Two treatments, represented in reciprocal space, are known to suppress the sloshing: (i) the inverse Kerker metric for Pulay optimization and (ii) Kerker-type preconditioning in mixing $R^{\mathrm{opt}}$. In all-electron methods, where the charge density does not have a converging Fourier representation, treatments equivalent or similar to (i) and (ii) have not been described so far. In this work, we show that, by going through the calculation of Hartree potential, one can accomplish the procedures (i) and (ii) without entering the reciprocal space. Test calculations are done with a FLAPW method. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B24.00011: Quest for a workhorse MGGA functional Bernard Delley A semi-empirical, numerically robust, parametrization of the exchange functional has been obtained by optimization of bond energies in a database of 500 species. The variables, density, gradient and kinetic energy density, can differentiate efficiently among the wide variety of bonds in the database. The resulting MGGA rivals the thermochmistry accuracy of composite quantum chemistry approaches when applied to a wider data set. But, not only, it also provides noticeable improvements over GGA's for solid state properties, including properties not obviously related to bonding energies. As an MGGA is not significantly more demanding computationally than a GGA, this MGGA may become the workhorse density functional for a wide range of applications. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B24.00012: First-Principles Investigation of Electronic Excitation Dynamics in Water under Proton Irradiation Kyle Reeves, Yosuke Kanai A predictive and quantitative understanding of electronic excitation dynamics in water under proton irradiation is of great importance in many technological areas ranging from utilizing proton beam therapy to preventing nuclear reactor damages. Despite its importance, an atomistic description of the excitation mechanism has yet to be fully understood. Identifying how a high-energy proton dissipates its kinetic energy into the electronic excitation is crucial for predicting atomistic damages, later resulting in the formation of different chemical species. In this work, we use our new, large-scale first-principles Ehrenfest dynamics method [1,2] based on real-time time-dependent density functional theory to simulate the electronic response of bulk water to a fast-moving proton. In particular, we will discuss the topological nature of the electronic excitation as a function of the proton velocity. We will employ maximally-localized functions to bridge our quantitative findings from first-principles simulations to a conceptual understanding in the field of water radiolysis. [1] ``Plane-wave Pseudopotential Implementation of Explicit Integrators for Time-Dependent Kohn-Sham Equations in Large Scale Simulations'' A. Schleife, E. W. Draeger, Y. Kanai, A. A. Correa, \underline {J. Chem. Phys., 137, 22A546 (2012)} [2] ``Quantum Dynamics Simulation of Electrons in Materials on High-Performance Computers'' A. Schleife, E. W. Draeger, V. Anisimov, A. A. Correa, Y. Kanai, \underline {Computing in Science and Engineering, 16 (5), 54} (2014). [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B24.00013: Strongly Constrained and Appropriately Normed (SCAN) Meta-Generalized Gradient Approximation for Exchange and Correlation Jianwei Sun, Adrienn Ruzsinszky, John Perdew Meta-generalized gradient approximations (meta-GGAs) construct the exchange-correlation (xc) energy density from the local electron density, its gradient, and the orbital kinetic energy density. They are the most accurate of the computationally-efficient semilocal density functionals. We construct a SCAN meta-GGA which satisfies all the known exact constraints that a meta-GGA can, including a new tight lower bound on the exchange energy [1]. SCAN is constructed as an interpolation/extrapolation on $\alpha $, the dimensionless variable that can recognize covalent single $(\alpha \approx 0)$, metallic ($\alpha \approx 1)$, and weak ($\alpha >>1)$ bonds [2]. A few parameters are included for appropriate norming on systems where a meta-GGA should be especially accurate due to xc hole localization. \\[4pt] [1] J.P. Perdew, A. Ruzsinszky, J. Sun. and K. Burke, J. Chem. Phys. 140, 18A533 (2014).\\[0pt] [2] J. Sun et al., Phys. Rev. Lett. 111, 106401 (2013). [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B24.00014: A Generalized Slave-Particle Method Alexandru Bogdan Georgescu, Sohrab Ismail-Beigi Two slave-particle methods, namely the slave-rotor and the slave-spin approaches, have been of recent interest in the computational correlated electron community. Both methods solve Hubbard-type models and go beyond the single-particle approximations by describing aspects of correlated electron behavior in a computationally efficient manner. We present a generalized slave-particle formalism that connects the the two while reproducing the results of each method in the appropriate limit. The framework automatically corrects the problematic small U behavior of the slave-rotor approach while reproducing its behavior in situations where it has been found physically relevant (e.g., for nickelate heterostructures). [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B24.00015: Selectively localized Wannier functions Runzhi Wang, Emanuel Lazar, Hyowon Park, Andrew Millis, Chris Marianetti Since the seminal work of Marzari and Vanderbilt, maximally localized Wannier functions have become widely used as real-space representations of electronic structure in periodic systems. In this talk we discuss selectively localized Wannier functions (SLWF) which allow localization of a particular subset of orbitals of interest, and also enable the fixing of orbital centers and ensuring the preservation of point-group symmetries. Applications of our method to GaAs, SrMnO$_3$, and Co demonstrate that SLWF can offer improvements over standard techniques, especially in beyond DFT methods. [Preview Abstract] |
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