Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G24: Electronic Structure Methods II 
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Sponsoring Units: DCOMP Chair: James Chelikowski, University of Texas at Austin Room: 203AB 
Tuesday, March 3, 2015 11:15AM  11:27AM 
G24.00001: Improved forces and nonlocal operators using high order integration Grady Schofield, N. Scott Bobbitt, Charles Lena, James R. Chelikowsky We present a new highorder modification to the finitedifference based real space pseudopotential density functional theory method. By giving a highorder treatment to the nonlocal pseudopotential terms in the Hamiltonian, as well as all quantities of interest obtained by postprocessing the wavefunctions, we improve the accuracy of total energy, interatomic forces, vibrational modes, and anharmonic effects. We demonstrate the power of this new technique by computing vibrational modes for a few common molecules containing atoms that are more difficult for highaccuracy force calculations, such as oxygen and nitrogen, due to the depth of the pseudopotential. The reduction in numerical noise as atoms move over the grid allows using a larger grid spacing than would be required with a conventional finite difference based discretization. Savings in both memory and computational time, due to a smaller spectral radius, will be discussed. [Preview Abstract] 
Tuesday, March 3, 2015 11:27AM  11:39AM 
G24.00002: Electronic correlation contributions to structural energies Roger Haydock The recursion method is used to calculate electronic excitation spectra including electronelectron interactions within the Hubbard model. The effects of correlation on structural energies are then obtained from these spectra and applied to stacking faults. http://arxiv.org/abs/1405.2288 [Preview Abstract] 
Tuesday, March 3, 2015 11:39AM  11:51AM 
G24.00003: Optimization Algorithm for the Generation of ONCV Pseudopotentials Martin Schlipf, Francois Gygi We present an optimization algorithm to construct pseudopotentials and use it to generate a set of Optimized NormConserving Vanderbilt (ONCV) pseudopotentials[1] for elements up to Z=83 (Bi) (excluding Lanthanides). We introduce a quality function that assesses the agreement of a pseudopotential calculation with allelectron FLAPW results, and the necessary planewave energy cutoff. This quality function allows us to use a NelderMead optimization algorithm on a training set of materials to optimize the input parameters of the pseudopotential construction for most of the periodic table. We control the accuracy of the resulting pseudopotentials on a test set of materials independent of the training set. We find that the automatically constructed pseudopotentials provide a good agreement with the allelectron results obtained using the FLEUR code [2] with a planewave energy cutoff of approximately 60 Ry. \\{} [1] D. R. Hamann, Phys. Rev. {\bf B88}, 085117 (2013).\\{} [2] FLEUR code, http://www.flapw.de\\{} [Preview Abstract] 
Tuesday, March 3, 2015 11:51AM  12:03PM 
G24.00004: MBTS Boundary Conditions in Continuous Systems G. A. Benesh, Roger Haydock Boundary conditions imposed on a local system that is joined to a larger substrate system often introduce unphysical reflections that affect eigenstate energies, densities of states, and charge densities. These problems are common in both atomic cluster and surface slab calculations. Solutions of the Schrodinger equation for the physical system do not possess such reflections; these wave functions carry current smoothly across the (artificial) boundary between the local system and the underlying medium. Previously, Haydock and Nex derived a nonreflecting boundary condition for discrete systems [Phys. Rev. B 75, 205121 (2006)]. Solutions satisfying this maximal breaking of timereversal symmetry (MBTS) boundary condition carry current away from the boundary at a maximal ratein much the same way as the exact wave functions for the physical system. The MBTS boundary condition has proved useful in discrete systems for constructing densities of states and other distributions from moments or continued fractions. The MBTS approach has now been extended to studies employing continuous spatial wave functions, including surface slab calculations and model systems. Results are compared with free slab calculations, embedding calculations, and experiment. [Preview Abstract] 
Tuesday, March 3, 2015 12:03PM  12:15PM 
G24.00005: Quantal Density Functional Theory (QDFT): Further Understandings Viraht Sahni, XiaoYin Pan, Tao Yang We consider electrons in the following external fields: (a) {\boldmath $\cal{E}$} $({\bf{r}}t)=$ {\boldmath $\nabla$ } $v ({\bf{r}}t)$, ${\bf{B}}({\bf{r}}t)=\nabla\times{\bf{A}}({\bf{r}}t)$, and ${\bf{E}}({\bf{r}}t)=\nabla\phi({\bf{r}}t)(1/c) \partial {\bf{A}}({\bf{r}}t)/\partial t$, (b) {\boldmath $\cal{E}$ } $({\bf{r}}t)=$ {\boldmath $\nabla$} $v({\bf{r}} t)$, (c) {\boldmath $\cal{E}$ } $({\bf{r}})=$ {\boldmath $\nabla$ } $v ({\bf{r}})$ and ${\bf{B}}({\bf{r}}t)=\nabla\times{\bf{A}}({\bf{r}} t)$, and (d) {\boldmath $\cal{E}$ } $({\bf{r}})=$ {\boldmath $\nabla$ } $v({\bf{r}})$. The basic variables for these systems are for (a) the density $\rho({\bf{r}}t)$ and physical current density ${\bf{j}}({\bf{r}} t)$, (b) $\rho({\bf{r}}t)$ and (paramagnetic) ${\bf{j}}({\bf{r}}t)$, (c) $\rho({\bf{r}})$ and ${\bf{j}}({\bf{r}})$, (d) $\rho ({\bf{r}})$. In QDFT, the local potential of the model fermions is the work done in a conservative effective field. In each of the above cases the effective field is representative of the \textit{same} correlations, \textit{viz}. due to the Pauli exclusion principle, Coulomb repulsion and CorrelationKinetic effects. [Preview Abstract] 
Tuesday, March 3, 2015 12:15PM  12:27PM 
G24.00006: Sum grequency generation spectroscopy from first principles Quan Wan, Giulia Galli Sum frequency generation (SFG) spectroscopy is widely used to study the structural and dynamical properties of surfaces and interfaces. Within the dipole approximation, SFG signals are solely determined by the surface, and bulk contributions vanish. However, the bulk portion of a material may contribute to SFG spectra through higher multipole excitations, e.g. quadrupole, which usually are difficult to separate in the measured spectra. Here we present a first principles theoretical framework, to compute SFG spectra of molecular solids and fluids. Within the dipole approximation, we computed the dipole and polarizability using maximally localized Wannier functions (MLWF) and density functional perturbation theory [1]. We then extended our method to include quadrupole contributions, and we computed quadrupole moments and their derivatives using MLWF and a realspace correction scheme [2], and an electric enthalpy functional. We applied our approach to investigate the ice Ih surface and we present results obtained by both finite differences and ab initio molecular dynamics [3] simulations. [1] Wan \textit{et al.} J. Chem. Theory Comput. 9, 4124 (2013) [2] Stengal \textit{et al.} Phys. Rev. B 73, 075121 (2006) [3] Qbox Code http://eslab.ucdavis.edu/software/qbox [Preview Abstract] 
Tuesday, March 3, 2015 12:27PM  12:39PM 
G24.00007: A first principles method for simulating phonons in strongly disordered materials Tom Berlijn, Olivier Delaire, Ben Larson At the microscopic level the flow of vibrational heat is encoded not only in the energies of phonons but also in their lifetimes. In many functional materials these phonon lifetimes are controlled by strong disorder. Such systems are difficult to understand from conventional perturbation theories or mean field treatments. Here we will present an affordable and accurate first principles method for simulating phonons in strongly disordered materials. The method will be illustrated with applications ranging from thermoelectrics to nuclear fuels. TB was supported as a Wigner Fellow at the Oak Ridge National Laboratory, OD was supported by the US DOEBES, Materials Science and Engineering Division, and BL was supported by the CMSNF Energy Frontier Research Center. [Preview Abstract] 
Tuesday, March 3, 2015 12:39PM  12:51PM 
G24.00008: RealSpace MultipleScattering Xray Absorption Spectroscopy Calculations of $d$ and $f$state Materials using a Hubbard Model Christian Vorwerk, Kevin Jorissen, John Rehr, Ahmed Towfiq We present calculations of the electronic structure and xray spectra of materials with correlated $d$ and $f$electron states treated with the Hubbard model in a realspace multiple scattering (RSMS) formalism, and using a rotationally invariant local density approximation (LDA+$U$). Values of the Hubbard parameter $U$ are calculated ab initio using the constrained randomphase approximation (cRPA). The realspace Green's function approach with Hubbard model corrections is an efficient way to describe localized electron states in strongly correlated systems, and their effect on corelevel xray spectra. The method is shown to give the correct density of states and xray absorption spectra for Transition Metal and Lanthanideoxides such as Ce2O3 and NiO, where the traditional RSMS calculations fail. [Preview Abstract] 
Tuesday, March 3, 2015 12:51PM  1:03PM 
G24.00009: Partial RayleighRitz procedure for quasiminimal basis sets Vincent MichaudRioux, Hong Guo Recent KohnSham DFT solver implementations [13] concentrate on building a subspace spanned by the occupied KohnSham orbitals via Chebyshev filtering [1]. The RayleighRitz procedure is generally performed to populate the KohnSham orbitals correctly and constitutes a major bottleneck in large electronic structure simulations. We found that the full diagonalization of the projected Hamiltonian can be avoided; only the partly occupied subspace is necessary since the fully occupied subspace can be obtained from the orthogonal complement of the former. For quasiminimal basis sets, the size of the eigenvalue problem can be reduced significantly at the cost of constructing an orthogonal complement. The method can also be used with nonminimal basis sets such as atomic orbitals by performing a second projection of the KohnSham Hamiltonian. The partial RayleighRitz procedure was implemented in our real space electronic structure calculator, which we used to conduct a performance comparison of the stateoftheart RayleighRitz procedure against the partial RayleighRitz procedure. [1] Zhou, et al., Phys. Rev. E 74, 066704 (2006). [2] Motamarri, et al., Journal of Computational Physics 253, 308 (2013). [3] Levitt, A. and Torrent, M., Computer Physics Communications, In Press (2014) [Preview Abstract] 
Tuesday, March 3, 2015 1:03PM  1:15PM 
G24.00010: Spectral function from Reduced Density Matrix Functional Theory Pina Romaniello, Stefano Di Sabatino, Jan A. Berger, Lucia Reining In this work we focus on the calculation of the spectral function, which determines, for example, photoemission spectra, from reduced density matrix functional theory. Starting from its definition in terms of the onebody Green's function we derive an expression for the spectral function that depends on the natural occupation numbers and on an effective energy [1] which accounts for all the charged excitations. This effective energy depends on the twobody as well as higherorder density matrices. Various approximations to this expression are explored by using the exactly solvable Hubbard chains [2]. \\[4pt] [1] J.A. Berger, L. Reining, and F. Sottile, Phys. Rev. B 82, 041103 (2010)\\[0pt] [2] S. Di Sabatino, J.A. Berger, L. Reining, and P. Romaniello, in preparation [Preview Abstract] 
Tuesday, March 3, 2015 1:15PM  1:27PM 
G24.00011: KohnSham Band Structure Benchmark Including SpinOrbit Coupling for 2D and 3D Solids William Huhn, Volker Blum Accurate electronic band structures serve as a primary indicator of the suitability of a material for a given application, e.g., as electronic or catalytic materials. Computed band structures, however, are subject to a host of approximations, some of which are more obvious (e.g., the treatment of the exchangecorrelation of selfenergy) and others less obvious (e.g., the treatment of core, semicore, or valence electrons, handling of relativistic effects, or the accuracy of the underlying basis set used). We here provide a set of accurate KohnSham band structure benchmarks, using the numeric atomcentered allelectron electronic structure code FHIaims combined with the ``traditional'' PBE functional and the hybrid HSE functional, to calculate core, valence, and lowlying conduction bands of a set of 2D and 3D materials. Benchmarks are provided with and without effects of spinorbit coupling, using quasidegenerate perturbation theory to predict spinorbit splittings. [Preview Abstract] 
Tuesday, March 3, 2015 1:27PM  1:39PM 
G24.00012: Self diffusion of water molecules simulated by model interatomic potentials determined by a combination of firstprinciples calculation and multicanonical ensembles: exchangecorrelation functional dependence Yoshihide Yoshimoto Water is an ubiquitous substance and is both scientifically and technologically important. In this study, the self diffusion of water molecules are simulated using KumagaiKawamuraYokokawa type interatomic potentials [1] whose parameters are determined by a combination of firstprinciples calculation and multicanonical ensembles [2,3]. Because of the property of multicanonical ensemble, the determined potentials keep the thermodynamics of the reference firstprinciples simulations to a maximum extent. The author used PBE, PBE0, B3LYP, and B3LYP with DFTD3 exchangecorrelation potentials for the reference firstprinciples calculations to determine the model parameters. The obtained diffusion coefficients significantly depend on the choice of the exchange correlation functionals and the combination of B3LYP and DFTD3 [4] produced the best agreement with the experimental one. \\[4pt] [1] N. Kumagai and K. Kawamura and T. Yokokawa, Mol. Simul. 12, 177 (1994).\\[0pt] [2] Y. Yoshimoto, J. Chem. Phys., 125, 184103 (2006).\\[0pt] [3] Y. Yoshimoto, J. Phys. Soc. Jpn., 79, 034602 (2010).\\[0pt] [4] S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys, 132, 154104 (2010). [Preview Abstract] 
Tuesday, March 3, 2015 1:39PM  1:51PM 
G24.00013: Quantum pressure in molecules and solids: Influence of magnetic fields and spinorbit coupling on electron localization Jianmin Tao, Shi Liu, Fan Zheng, Andrew M. Rappe The most important concept in chemistry is chemical bond, which has been used by chemists to explain the properties of molecules and solids as well as chemical processes. Considerable efforts~[1,2] have been made toward a simple and yet fundamental understanding of this concept. Here we formulate the quantum pressure in an external magnetic field, allowing us to study the influence of magnetic fields and spinorbit coupling on electron localization in molecules and solids. We find that electrons in conjugated molecules become more localized in strong magnetic fields, due to the induced currents. We demonstrate that the quantum pressure not only can reveal electronic shell structures of atoms~[3], but also can be used to visualize bonding structures of molecules and solids, significantly extending the applicability of this descriptive tool. \\[4pt] [1] A.D. Becke and K.E. Edgecombe, J. Chem. Phys. 92, 5397 (1990).\\[0pt] [2] A. Savin, R. Nesper, S. Wengert, and T.F. F\"assler, Angew. Chem. Int. Ed. Engl. 36, 1808 (1997).\\[0pt] [3] J. Tao, G. Vignale, and I.V. Tokatly, Phys. Rev. Lett. 100, 206405 (2008). [Preview Abstract] 

G24.00014: ABSTRACT WITHDRAWN 
Tuesday, March 3, 2015 2:03PM  2:15PM 
G24.00015: Firstprinciples study of twodimensional electride: Yttrium carbide Chandani Nandadasa, Sungho Kim, SeongGon Kim, Young Lee, Sung Kim Electrides are an exclusive class of ionic compounds in which electrons serve as anions. We have performed firstprinciples density functional theory (DFT) calculations to investigate the structural, electronic and magnetic properties of twodimensional layeredstructure yttrium carbide (Y$_{2}$C). Generalized gradient approximation (GGA) with Projector Augmented Potentials (PAW) was used to obtain optimized lattice parameters, energy band structure, charge density and density of states (DOS) plots for Y$_{2}$C. The theoretically predicted structure of Y$_{2}$C is in good agreement with the experimental results. The band crossing the Fermi energy level proved that Y$_{2}$C has metallic properties. Additionally projected electronic density of states profiles were obtained to identify the electronic contribution from Y, C and nonatomic orbital located in interstitial site. The results of these calculations indicate that the presence of trapped electrons within the Y$_{2}$C interlayers. Furthermore, surface energies of YY and YC were calculated and charge densities were plotted with these surfaces. Magnetization density plots were used to obtain magnetic properties. [Preview Abstract] 
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