Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V13: Focus Session: Frontiers in Electronic Structure Theory III |
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Sponsoring Units: DCP DCOMP Chair: Wei Ku, Brookhaven National Laboratory Room: Morial Convention Center 204 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V13.00001: Dielectric Properties of Ice and Liquid Water from First Principle Calculations Deyu Lu, Francois Gygi, Giulia Galli We present a first-principle study of the dielectric properties of ice and liquid water. The eigenmodes of the dielectric matrix, $\epsilon^{-1}$, are analyzed in terms of maximally localized dielectric functions similar, in their definition, to maximally localized Wannier orbitals obtained from Bloch eigenstates of the electronic Hamiltonian. We show that the lowest eigenmodes of $\epsilon^{-1}$ are localized in real space and can be separated into groups related to the screening of lone-pairs, intra-, and inter-molecular bonds, respectively. The local properties of the dielectric matrix can be conveniently exploited to build approximate dielectric matrices for efficient, yet accurate calculations of quasiparticle energies. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V13.00002: Strong hybridization of Frenkel excitons in Mott insulators: a novel Wannier function perspective* Chi-Cheng Lee, H. C. Hsueh, Wei Ku Linear response scheme of the time-dependent density-functional theory (TDDFT) has been quite successful in the study of the excitations of weakly correlated systems. However, its applicability to strongly correlated systems remains unclear, especially due to the poor quality of the exchange-correlation kernel essential for those systems. On the other hand, the local-density approximation + Hubbard U (LDA+U) approximation has been shown to describe quite successfully the ground-state properties and electronic band structures of Mott insulators. Therefore, it is timely to investigate the linear response of the LDA+U functional in the framework of TDDFT in describing excitations of strongly correlated systems. In this talk, a theoretical (diagrammatic) framework of the linear response of LDA+U (TDLDA+U) functional will be presented and applied to the study of Frenkel excitons in NiO within the first-principles Wannier basis. The advantages and disadvantages of LDA+U functional will be discussed, in comparison with more advanced many-body approaches. [1] B. C. Larson, et al. PRL 99, 026401 (2007)*Work supported by U.S. DOE - CMSN [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V13.00003: Propagation of strongly bound Frenkel excitons in LiF: An effective two-particle kinematic approach of super-atom in ab initio Wannier basis Chen-Lin Yeh, Hung-Chung Hsueh, Wei Ku A general new first-principles Wannier function based method is proposed to better understand the propagation of strongly bound Frenkel excitions. Specifically, long-standing debate of the Frenkel nature of the excitons in LiF is made apparent by the formation of a ``super-atom'' consisting of Wannier orbitals from both Li and F. On this basis, a new approach is proposed by formulating the kinematic contribution to the propagation of the exciton via an effective two-particle hopping kernel. The same kernel contains both the mass enhancement at strong binding and the decay into continuum at weak binding, and is thus exact in both limits. This kinematic effect is compared with found to overwhelm the conventional interaction-based propagations of exciton in LiF. This general theoretical framework can be directly applied to the study of propagation of local excitations of strongly correlated systems. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V13.00004: Ab-initio Total Energy Calculation for Full-potential Multiple Scattering Theory Methods Yang Wang, Aurelian Rusanu, Malcolm Stocks, Don Nicholson, Markus Eisenbach The {\it ab initio} methods (e.g., KKR, KKR-CPA, LSMS) based on multiple scattering theory have the clear advantage of being able to calculate the Green function in a straightforward manner, which has important implications in the application of electronic structure calculations. But these methods have mostly been implemented within muffin-tin approximations. Recent advances in the numerical implementation of full- potential multiple scattering theory and, in particular, the development of an innovative Poisson equation solver have made carrying out the fully self-consistent full-potential calculation possible. In this presentation, we discuss various implementations of the full-potential total energy calculation, and we investigate the convergence of the total energy with respect to the angular momentum expansion cutoff for scattering matrices. Finally, we compare the full-potential total energy with the muffin-tin approximation results. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V13.00005: A quantum chemistry roadmap towards highly accurate adsorption energies at ionic surfaces Bo Li, Angelos Michaelides, Matthias Scheffler A roadmap is established to compute adsorption energies of molecules at ionic surfaces with an accuracy approaching chemical accuracy (a precision of 1 kcal/mol or $\sim$43 meV). The approach relies on established quantum chemistry methodologies and involves a separation of the total adsorption energy into contributions from Hartree-Fock and electron correlation, the use of embedded cluster models of the substrate, and extrapolations to the complete basis set limit. Application of the procedure to the example of water on salt, with electron correlation treated at the CCSD(T) level, yields an adsorption energy for a water monomer on NaCl(001) of 480 $\pm$ 20 meV. [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V13.00006: Surface energies of semiconductors by the energy density method Min Yu, Richard M. Martin Energy Density formalism within the first-principles pseudopotential density functional theory has been proposed by Chetty and Martin$^{1}$ in 1990s. Although the energy density function is non-unique, nevertheless integrals over surface regions provide unique results for surface energies, and calculations have been carried out by several groups$^{2,3}$ to study the polar surfaces and interfaces of solid state systems such as GaAs $(111)$ and $(\bar{1}\bar{1}\bar{1})$ polar surfaces. In our work, we apply this method to wurtzite CdSe to determine the energy of of various polar surfaces such as $(0001),(000\bar{1})$, and non-polar surfaces such as $(10\bar{1}0),(11\bar{2}0)$, from which we can estimate the equilibrium crystal shape for large nanoclusters. 1. N. Chetty and Richard M. Martin, Phys. Rev. B 45, 6074 (1992). 2. K. Rapcewicz, B. Chen, B. Yakobson, and J. Bernholc, Phys. Rev. B 57, 7281 (1998). 3. N. Moll, A. Kley, E. Pehlke, and M. Scheffler, Phys. Rev. B 54, 8844 (1996). [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 1:03PM |
V13.00007: Electron-phonon interaction using Wannier functions: from single-layer graphene to cuprate superconductors Invited Speaker: Feliciano Giustino The interaction between electrons and phonons is central to many phenomena, including electrical and thermal transport and superconductivity. Recently the electron-phonon (e-ph) interaction has been the focus of intense research efforts in the physics of high-temperature superconductivity and nanoscale transport. Despite the continued interest in the e-ph problem, first-principles calculations remain challenging due to the large computational effort required to describe e-ph scattering processes in the proximity of the Fermi surface. In this talk I will present a method based on Wannier functions which greatly reduces the computational cost of e-ph calculations [1,2]. The underlying idea is to exploit the spatial localization of electrons and phonons in the maximally localized Wannier representation. After describing the method I will review recent applications to materials of current interest. I will discuss how the e-ph interaction affects the dynamics of Dirac fermions in graphene [3], the origin of superconductivity in boron-doped diamond [1], and the relation between Fermi surface topology and superconductivity in super-hard carbides. I will conclude this presentation by discussing the role of phonons in the angle-resolved photoemission spectra of cuprates [4]. \newline [1] F. Giustino, J.R. Yates, I. Souza, M.L. Cohen, and S.G. Louie, Phys. Rev. Lett. 98, 047005 (2007). \newline [2] F. Giustino, M.L. Cohen, and S.G. Louie, Phys. Rev. B 76, 165108 (2007). \newline [3] C.-H. Park, F. Giustino, M.L. Cohen, and S.G. Louie, Phys. Rev. Lett. 99, 086804 (2007). \newline [4] F. Giustino, M.L. Cohen, and S.G. Louie, http://arXiv:0710.2146. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V13.00008: Ensemble density functional theory, the atom-in-molecule problem, and reactive charge transfer Susan Atlas, Steven Valone A major challenge in large-scale simulations of complex biomolecular and materials systems is the ability to accurately describe reactive dynamics. We have previously described a new multiscale formalism, based on density functional theory and the embedded-atom method, that enables the rigorous encoding of quantum mechanical excitation effects such as charge polarization and charge transfer within a classical potential. Here we describe a new formulation of a key element of the theory: the deconstruction of molecular densities into subsystem atom-in-molecule components via ensemble constrained-search density functional theory. The method is implemented via the self-consistent solution of coupled sets of Kohn-Sham equations in conjunction with chemical potential equalization across subsystems. This leads to a natural interpretation of dynamical charge transfer and charge polarization in terms of an electronic entropy, thus extending the seminal work of Gross, Oliveira, and Kohn (1988). [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V13.00009: Correction of Finite Size Errors in Many-body Electronic Structure Calculations Hendra Kwee, Shiwei Zhang, Henry Krakauer Finite-size (FS) effects are a major source of error in many-body (MB) electronic structure calculations of extended systems. Reducing FS errors is thus a key to broader applications of MB methods in real materials, and the subject has drawn considerable attention.\footnote{P. R. C. Kent \textit{et. al.}, Phys. Rev. B \textbf{59}, 1917 (1999); S. Chiesa \textit{et. al.} Phys. Rev. Lett. \textbf{97}, 076404 (2006).} We show that MB FS effects can be effectively included in a modified local density approximation calculation. A parametrization for the FS exchange-correlation functional is obtained. The method is simple and gives post-processing corrections that can be applied to any MB results. Conceptually, it gives a consistent framework for relating FS effects in MB and DFT calculations, which is important if the two methods are to be seamlessly interfaced to bridge length scales. Applications to a model insulator (P$_2$ in a supercell), to semiconducting Si, and to metallic Na show that the method delivers greatly improved FS corrections.\footnote{H.\,Kwee, S.\,Zhang and H.\,Krakauer (2007), preprint at http://arxiv.org/abs/0711.0921.} [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V13.00010: Embedding quantum-mechanics in an interatomic potential simulation using local energies Noam Bernstein, Gabor Csanyi Atomistic simulations that use quantum-mechanical total-energy models provide high accuracy and reliability at the price of computational expense. Classical approximations such as interatomic potentials are much faster, but less transferable. We couple the two approaches concurrently, to describe part of the system quantum-mechanically and part with interatomic potentials, using a weighted sum of atomic energies. This enables us to compute a {\em well defined total energy} for the hybrid system with small and controllable errors caused by the boundaries of the QM region. Using tight-binding as a model quantum-mechanical method, we can efficiently evaluate the derivatives of the total energy, including the effects of charge self-consistency, enabling an energy conserving molecular dynamics simulation for a fixed QM region. We show that a localized quantum-mechanical atomic energy can be defined, and that this energy is physically meaningful. We present tests of the method, and discuss convergence with respect to various method parameters, and the effects of moving the QM region during the dynamics. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V13.00011: The search for minimum-energy atomic configurations on a lattice: Lamarckian twist on Darwinian Evolution Mayeul d'Avezac, Alex Zunger We examine how two different mechanisms proposed historically for biological evolution compare for the determination of crystal structures from random initial lattice-configurations. The Darwinian theory of evolution contends that the genetic makeup inherited at birth is the one passed on to offsprings. Lamarck surmised additionally that offspring can inherit acquired traits. In the case of lattice-configurations, such improvements consist in A$\leftrightarrow$B transmutations of atomic sites as guided by ``Virtual Atom'' energy-gradients({\small M. d'Avezac and Alex Zunger, J. Phys.: Cond. Matt. {\bf 19}, 402201 (2007)}). This hybrid evolution is shown to provide an efficient solution to a generalized Ising Hamiltonian, illustrated by finding the ground-states of face-centered cubic Au$_{1-x}$Pd$_x$ using a cluster-expansion functional fitted to first-principles total-energies. For example, finding all minimum-energy structures of a 32-atom supercell with $95\,\%$ confidence requires evaluating $750, 000$ configurations using local improvements only, $150, 000$ using a reciprocal-space genetic algorithm only, and $14,000$ using the hybrid approach. We consider applying the lamarckian search to further functionals. [Preview Abstract] |
Thursday, March 13, 2008 1:51PM - 2:03PM |
V13.00012: Using genetic algorithms to find from first-principles the minimum-energy crystal structure starting from random cell vectors and random atomic positions. G. Trimarchi, M. D'Avezac, Alex Zunger We address the global space-group optimization problem in binary metallic A$_{q}$B$_{1-q}$ alloys using an evolutionary algorithm. A set of crystal structures with randomly-selected lattice vectors and atomic positions is evolved, replacing the highest energy structures with new ones generated through mating or mutation, as well as ab-initio structural relaxation to the nearest local minimum. This was applied to a few compounds whose lattice-type is difficult to guess because the constituent solids A and B have different lattice types (e.g., A is fcc and B is bcc): (i) compounds with the crystal lattice of either A or B constituents, i.e., CdPt$_{3}$, AlSc$_{3}$, Al$_{3}$Sc; (ii) compounds with a crystal lattice different than that of either constituents, i.e., AlSc and CuPd; (iii) compounds whose crystal lattice is not even of a Bravais type, e.g., PdTi$_{3}$. The optimization scheme retrieved the lowest energy structures within about 100 total-energy evaluations. Not all independent GA sequences end up giving the same final structure; we select the lowest energy structure from all sequences. Using a model calculation, we will discuss how many independent GA sequences are needed to find the lowest energy structure with given confidence. [Preview Abstract] |
Thursday, March 13, 2008 2:03PM - 2:15PM |
V13.00013: From grand-canonical density functional theory towards rational compound design Anatole von Lilienfeld The fundamental challenge of rational compound design, ie the reverse engineering of chemical compounds with predefined specific properties, originates in the high-dimensional combinatorial nature of chemical space. Chemical space is the hyper-space of a given set of molecular observables that is spanned by the grand-canonical variables (particle densities of electrons and nuclei) which define chemical composition. A brief but rigorous description of chemical space within the molecular grand-canonical ensemble multi-component density functional theory framework will be given [1]. Numerical results will be presented for intermolecular energies as a continuous function of alchemical variations within a neutral and isoelectronic 10 proton system, including CH$_4$, NH$_3$, H$_2$O, and HF, interacting with formic acid [2]. Furthermore, engineering the Fermi level through alchemical generation of boron-nitrogen doped mutants of benzene shall be discussed [3].\newline [1] von Lilienfeld and Tuckerman {\em JCP} {\bf 125} 154104 (2006)\newline [2] von Lilienfeld and Tuckerman {\em JCTC} {\bf 3} 1083 (2007)\newline [3] Marcon et al. {\em JCP} {\bf 127} 064305 (2007) [Preview Abstract] |
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