Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T36: Frontiers in Electronic Structure Theory |
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Sponsoring Units: DCP DCOMP Chair: Brian Landry, Harvard University Room: 408 |
Wednesday, March 18, 2009 2:30PM - 2:42PM |
T36.00001: New approach on calculating Green's functions in Full-Potential Multiple Scattering Methods. Aurelian Rusanu, Yang Wang, G. M. Stocks, John S. Faulkner The most common methods of computing Green's functions in modern full-potential multiple scattering applications rely on solving Schr\"{o}dinger (Dirac) equations for regular and irregular solutions of a single-site scatterer over an energy contour in the complex plane. While, for spherical potentials, the standard formulae for calculating the Green's function are numerically stable they often result in unphysical behavior for non spherical potentials, particularly close to the nucleus and for large angular momentum quantum numbers. Here we use a new analytical and numerical method that does not require calculation of the irregular solution, to which the numerical instability can be traced. The new approach results in the correct analytic behavior and numerical stability. [Preview Abstract] |
Wednesday, March 18, 2009 2:42PM - 2:54PM |
T36.00002: Local excitations in charge-transfer insulators: a super atom approach via Wannier functions Chi-Cheng Lee, Weiguo Yin, Wei Ku Local excitations in strongly correlated charge-transfer insulator are very often tied to the rich functionalities of these materials. However, these tightly bound local excitations prove to be difficult to calculate from first-principles. In particular, the strong local interactions render the typical first-principles perturbation approach (via diagrammatic Bethe-Salpeter equation) inapplicable to describe the multiplets. In this talk, our recent progress in evaluating the local excitations in NiO will be presented. Utilizing the gauge freedom of the Wannier functions, the oxygen (charge-transfer) degrees of freedom can be integrated into a ``super atom'', in which the strong local interactions can be incorporated on the equal footing as the strong coupling between the oxygen p- and Ni d- orbitals. Our results lead to good agreement with recent non-resonant inelastic X-ray scattering data [1] and the cluster calculation [2] for both q-dependence and excitation energies. Finally, extension to propagation of the local excitation will be addressed to include the dispersion in momentum space. [1] B. C. Larson et al, PRL 99, 026401 (2007) [2] M. W. Haverkort et al, PRL 99, 257401 (2007) [Preview Abstract] |
Wednesday, March 18, 2009 2:54PM - 3:06PM |
T36.00003: Self-healing diffusion quantum Monte Carlo algorithms: Theory and Applications F.A. Reboredo, P.R.C. Kent, M.L. Tiago, R.Q. Hood We present a method to obtain the fixed node ground state wave function from an importance sampling Diffusion Monte Carlo (DMC) run. The fixed node ground state wave-function is altered to obtain an improved trial wave-function for the next DMC run. The theory behind this approach will be discussed. Two iterative algorithms are presented and validated in a model system by direct comparison with full configuration interaction (CI) wave functions and energies. We find that the trial wave-function is systematically improved. The scalar product of the trial wave-function with the CI result converges to 1 even starting from wave-functions orthogonal to the CI ground state. Similarly, the DMC total energy and density converges to the CI result. In the optimization process we find an optimal non-interacting nodal potential of density-functional-like form. An extension to a model system with full Coulomb interactions demonstrates that we can obtain the exact Kohn-Sham effective potential from the DMC data. Subsequently we apply our method to real molecules such as benzene and find that we can improve the ground state energy as compared with the single determinant result even starting from random wave-functions. Results for other molecular systems and comparison with alternative methods will be presented. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T36.00004: Removal of residual nonspherical self-interaction error in LDA+$U$ Fei Zhou, Vidvuds Ozolins In the established LDA+$U$ method, the electron self-interaction, which is generally nonspherical and orbital-dependent, is removed in a mean-field way. This results in residual self-interaction errors, particularly pronounced for $f$-electrons. An alternative double counting scheme that modifies the exchange, not Hartree, energy of LDA is proposed as a remedy. We show that LDA+$U$ with our approach preserves the expected degeneracy of $f^1$ and $f^2$ states in free ions and the correct ground states in the PrO$_2$ solid. [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T36.00005: The $f$-electron challenge: localized and itinerant states in lanthanide oxides united by $GW$@LDA+$U$ Matthias Scheffler, Hong Jiang, Ricardo I. Gomez-Abal, Patrick Rinke Understanding the physics of $f$-electron systems, characterized by the competition between itinerant (delocalized) and highly localized $f$-states, is regarded as a great challenge in condensed-matter physics today. As a first step towards a systematic \textit{ab initio} understanding of $f$-electron systems, we apply many-body perturbation theory in the $G_0W_0$ approach based on LDA+$U$ ground state calculations ($G_0W_0$@LDA+$U$) to a selected set of lanthanide oxides (CeO$_2$ and Ln$_2$O$_3$ (Ln=lanthanide series)). These compounds have important technological applications, in particular in catalysis and microelectronics. We demonstrate good agreement between the $G_0W_0$ density of states (DOS) and experimental spectra for CeO$_2$ and Ce$_2$O$_3$. For the whole Ln$_2$O$_3$ series $G_0W_0$@LDA+$U$ reproduces all main features found for the optical experimental band gaps. Inspection of the DOS reveals that the relative positions of the occupied and unoccupied $f$-states predicted by $G_0W_0$ confirm the experimental conjecture derived from phenomenological arguments. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T36.00006: Self-interaction correction in multiple scattering theory -- Application to transition metal oxide Markus Daene, Wolfram Hergert, Arthur Ernst, Martin Lueders, Zdzislawa Szotek, Walter Temmerman In this work we study the electronic structure of 3d-transition metal oxides as obtained with the self-interaction corrected-local spin density approximation method, implemented within multiple scattering theory. We briefly describe the formalism and discuss important technical issues of its implementation within the KKR band structure method.\\ We present results of such important properties as lattice constants, local magnetic moments, band gaps and discuss them in comparison with the LSD and the experimental values. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T36.00007: Computational Modeling of Actinide Complexes Pertinent to Environment Krishnan Balasubramanian We discuss computational projects relevant to actinide separation, complexes and the possibility of actinide sequestration by engineered mesoporous materials We have carried out computational studies on a number of actinide complexes in aqueous solution; as such complexes are of considerable importance in our understanding of behavior of actinide species in the environment and high level nuclear waste, especially experimental-theoretical collaboration on curium (III) complexes with multi-dentate ligands with Nitsche and coworkers at LBNL. Cu(III) complexes with phosphonic acid (PPA) were studied for assessing relative binding strengths of the two ligands with varying pH. Possible isomers of CmH2PPA2+ and CmHPPA+ complexes were computed both in the gas phase and aqueous solution and the results of spectra and geometry will be discussed. The effects of the aqueous solvent in the configuration preferences of CmH2PPA2+ and We have also studied aqueous complexes of U(VI), Np(VI) and Pu(VI) with OH-. We will discuss the results of out extensive \textit{ab initio} computations on the equilibrium structure, infrared spectra, and bonding characteristics of a variety of hydrated NpO2(CO3)$m ^{q-}$ complexes by considering the solvent as a polarizable dielectric continuum as well as the corresponding anhydrate complexes in the gas-phase. The work at CSU Eastbay was supported in part by Office of Basic Energy Sciences of DOE, and the work at LLNL was carried out under contract number W-7405-Eng-48. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T36.00008: The converse approach to NMR chemical shifts from first-principles: application to finite and infinite aromatic compounds T. Thonhauser, D. Ceresoli, N. Marzari We present first-principles, density-functional theory calculations of the NMR chemical shifts for polycyclic aromatic hydrocarbons, starting with benzene and increasing sizes up to the one- and two-dimensional infinite limits of graphene ribbons and sheets. Our calculations are performed using a combination of the recently developed theory of orbital magnetization in solids, and a novel approach to NMR calculations where chemical shifts are obtained from the derivative of the orbital magnetization with respect to a microscopic, localized magnetic dipole. Using these methods we study on equal footing the $^1$H and $^{13}$C shifts in benzene, pyrene, coronene, in naphthalene, anthracene, naphthacene, and pentacene, and finally in graphene, graphite, and an infinite graphene ribbon. Our results show very good agreement with experiments and allow us to characterize the trends for the chemical shifts as a function of system size. [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T36.00009: NMR chemical shifts from first-principles using the converse approach in periodic boundary conditions Davide Ceresoli, Timo Thonhauser, Nicola Marzari An alternative, converse approach to the first-principles calculation of NMR shielding tensors can be formulated where NMR chemical shift are obtained from the derivative of the orbital magnetization with respect to the application of a microscopic, localized magnetic dipole. We apply here the modern theory of orbital magnetization to validate this formalism to the case of extended systems in periodic boundary conditions, finding very good agreement with established methods and experimental results. These results underscore the advantages of the converse approach over existing methods: (1) it can be applied to either isolated or periodic systems, (2) it avoids any linear response calculation, allowing to treat systems containing hundreds of atoms, and (3) it is not plagued by the gauge-origin problem. [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T36.00010: MP2 and RPA applied to solid state systems Martijn Marsman, Andreas Grueneis, Judith Harl, Georg Kresse We present {\it ab initio} total energy calculations at the level of Hartree-Fock + 2nd-order M\o ller-Plesset perturbation theory (HF+MP2), and the random-phase-approximation within the framework of the adiabatic-fluctuation-dissipation-theorem (ACFDT-RPA), for extended systems under periodic boundary conditions, using plane wave basis sets. We characterize and compare the accuracy of these methods with respect to their description of the lattice constants, bulk moduli, and atomizations energies of several archetypical solid state systems. Furthermore we present calculations of HF+MP2 quasiparticle gaps and compare them to results obtained within the GW approximation to the electronic self-energy. [Preview Abstract] |
Wednesday, March 18, 2009 4:30PM - 4:42PM |
T36.00011: Bridging the size gap between density-functional and many-body perturbation theory Paolo Umari The calculation of quasi-particle spectra based on the GW approximation is extended to systems of hundreds of atoms and the calculation of empty states is avoided. This is achieved through an optimal strategy, based on the use of Wannier-like orbitals, for obtaining a basis for the polarization propagator. Then, a Lanczos chain approach permits to calculate the self-energy. Our method is validated by calculating the vertical ionization energies of the benzene molecule and the band structure of crystalline silicon. Its potentials are then demonstrated by addressing the quasi-particle spectrum of models of vitreous materials, as well as of large organic molecules. [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T36.00012: Quasiparticle properties of DNA bases from GW calculations in a Wannier basis Xiaofeng Qian, Nicola Marzari, Paolo Umari The quasiparticle GW-Wannier (GWW) approach [1] has been recently developed to overcome the size limitations of conventional planewave GW calculations. By taking advantage of the localization properties of the maximally-localized Wannier functions and choosing a small set of polarization basis we reduce the number of Bloch wavefunctions products required for the evaluation of dynamical polarizabilities, and in turn greatly reduce memory requirements and computational efficiency. We apply GWW to study quasiparticle properties of different DNA bases and base-pairs, and solvation effects on the energy gap, demonstrating in the process the key advantages of this approach. [1] P. Umari,G. Stenuit, and S. Baroni, cond-mat/0811.1453 [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:06PM |
T36.00013: Reliable Prediction of Charge Transfer Excitations in Molecular Complexes Leeor Kronik, Tamar Stein, Roi Baer We show how charge transfer excitations at molecular complexes can be calculated quantitatively using time-dependent density functional theory (DFT). Predictive power is obtained from range -separated hybrid functionals using non-empirical tuning of the range-splitting parameter. Excellent performance of this approach is obtained for a series of complexes composed of various aromatic donors and the tetracyanoethylene (TCNE) acceptor, paving the way to systematic non-empirical quantitative studies of charge-transfer excitations in real systems. [Preview Abstract] |
Wednesday, March 18, 2009 5:06PM - 5:18PM |
T36.00014: Transcorrelated method applied to solids: numerical assessment of the SCF effect Keitaro Sodeyama, Rei Sakuma, Shinji Tsuneyuki To calculate the electronic structures of solids including
electron correlation effects, we have developed the
transcorrelated (TC) method which was first proposed by Boys and
Handy. In the TC method, the wave function is represented by a
correlated wave function $F \Phi$, where $\Phi$ is a single
Slater determinant and $F$ is a Jastrow function,
$F=\exp[-\sum_{i |
Wednesday, March 18, 2009 5:18PM - 5:30PM |
T36.00015: Unique assignment of energy to atoms in a solid Min Yu, Dallas R. Trinkle, Richard M. Martin We propose a way to decompose the total energy in a material into the contribution associated with each of the atoms, using the first-principles energy density formalism [1]. Although the energy density function is non-unique up to a gauge transformation, it has been used to calculate surface energies by integrals over cells chosen by symmetry [1] or over Voronoi polyhedra [2]. Bader charge analysis [3] partitions space into regions with a unique intergrated energy for any system with no requirements of symmetry. We implement the energy density method in the Vienna ab initio simulation package (VASP [4]) for both US-PP and PAW. We calculate energies for the Si (111), GaAs (110) nonpolar and (111) polar surfaces; vacancies and interstitials in Si and Al; and O in Ti. [1] N. Chetty and Richard M. Martin, Phys. Rev. B 45, 6074 (1992). [2] K. Rapcewicz, et al., Phys. Rev. B 57, 7281-7291(1998). [3] R. F. W. Bader, Atoms in Molecules: A Quantum Theory (1990). [4] G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999). [Preview Abstract] |
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