The Experts below are selected from a list of 13176 Experts worldwide ranked by ideXlab platform
Pablo Garciarisueno - One of the best experts on this subject based on the ideXlab platform.
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a survey of the parallel performance and accuracy of poisson solvers for electronic structure calculations
Journal of Computational Chemistry, 2014Co-Authors: Pablo Garciarisueno, Joseba Alberdirodriguez, Micael J T Oliveira, Xavier Andrade, Michael Pippig, Javier Muguerza, A Arruabarrena, Angel RubioAbstract:We present an analysis of different methods to calculate the classical electrostatic Hartree Potential created by charge distributions. Our goal is to provide the reader with an estimation on the performance—in terms of both numerical complexity and accuracy—of popular Poisson solvers, and to give an intuitive idea on the way these solvers operate. Highly parallelizable routines have been implemented in a first-principle simulation code (Octopus) to be used in our tests, so that reliable conclusions about the capability of methods to tackle large systems in cluster computing can be obtained from our work. © 2013 Wiley Periodicals, Inc.
Angel Rubio - One of the best experts on this subject based on the ideXlab platform.
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a survey of the parallel performance and accuracy of poisson solvers for electronic structure calculations
Journal of Computational Chemistry, 2014Co-Authors: Pablo Garciarisueno, Joseba Alberdirodriguez, Micael J T Oliveira, Xavier Andrade, Michael Pippig, Javier Muguerza, A Arruabarrena, Angel RubioAbstract:We present an analysis of different methods to calculate the classical electrostatic Hartree Potential created by charge distributions. Our goal is to provide the reader with an estimation on the performance—in terms of both numerical complexity and accuracy—of popular Poisson solvers, and to give an intuitive idea on the way these solvers operate. Highly parallelizable routines have been implemented in a first-principle simulation code (Octopus) to be used in our tests, so that reliable conclusions about the capability of methods to tackle large systems in cluster computing can be obtained from our work. © 2013 Wiley Periodicals, Inc.
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A survey of the parallel performance and the accuracy of Poisson solvers for electronic structure calculations
arXiv: Computational Physics, 2012Co-Authors: Pablo García-risueño, Micael J T Oliveira, Xavier Andrade, Michael Pippig, Javier Muguerza, A Arruabarrena, Joseba Alberdi-rodriguez, Angel RubioAbstract:We present an analysis of different methods to calculate the classical electrostatic Hartree Potential created by charge distributions. Our goal is to provide the reader with an estimation on the performance ---in terms of both numerical complexity and accuracy--- of popular Poisson solvers, and to give an intuitive idea on the way these solvers operate. Highly parallelisable routines have been implemented in the first-principle simulation code Octopus to be used in our tests, so that reliable conclusions about the capability of methods to tackle large systems in cluster computing can be obtained from our work.
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Time and energy-resolved two photon-photoemission of the Cu(100) and Cu(111) metal surfaces
arXiv: Materials Science, 2003Co-Authors: Daniele Varsano, Miguel A. L. Marques, Angel RubioAbstract:We present calculations on energy- and time-resolved two-photon photoemission spectra of images states in Cu(100) and Cu(111) surfaces. The surface is modeled by a 1D effective Potential and the states are propagated within a real-space, real-time method. To obtain the energy resolved spectra we employ a geometrical approach based on a subdivision of space into two regions. We treat electronic inelastic effects by taking into account the scattering rates calculated within a GW scheme. To get further insight into the decaying mechanism we have also studied the effect of the variation of the classical Hartree Potential during the excitation. This effect turns out to be small.
Heinz-jürgen Flad - One of the best experts on this subject based on the ideXlab platform.
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Tensor decomposition in electronic structure calculations on 3D Cartesian grids
Journal of Computational Physics, 2009Co-Authors: Boris N. Khoromskij, Venera Khoromskaia, Sambasiva Rao Chinnamsetty, Heinz-jürgen FladAbstract:In this paper, we investigate a novel approach based on the combination of Tucker-type and canonical tensor decomposition techniques for the efficient numerical approximation of functions and operators in electronic structure calculations. In particular, we study applicability of tensor approximations for the numerical solution of Hartree-Fock and Kohn-Sham equations on 3D Cartesian grids. We show that the orthogonal Tucker-type tensor approximation of electron density and Hartree Potential of simple molecules leads to low tensor rank representations. This enables an efficient tensor-product convolution scheme for the computation of the Hartree Potential using a collocation-type approximation via piecewise constant basis functions on a uniform nxnxn grid. Combined with the Richardson extrapolation, our approach exhibits O(h^3) convergence in the grid-size h=O(n^-^1). Moreover, this requires O(3rn+r^3) storage, where r denotes the Tucker rank of the electron density with r=O(logn), almost uniformly in n. For example, calculations of the Coulomb matrix and the Hartree-Fock energy for the CH"4 molecule, with a pseudoPotential on the C atom, achieved accuracies of the order of 10^-^6 Hartree with a grid-size n of several hundreds. Since the tensor-product convolution in 3D is performed via 1D convolution transforms, our scheme markedly outperforms the 3D-FFT in both the computing time and storage requirements.
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tensor product approximation with optimal rank in quantum chemistry
Journal of Chemical Physics, 2007Co-Authors: Sambasiva Rao Chinnamsetty, Boris N. Khoromskij, Mike Espig, Wolfgang Hackbusch, Heinz-jürgen FladAbstract:Tensor product decompositions with optimal separation rank provide an interesting alternative to traditional Gaussian-type basis functions in electronic structure calculations. We discuss various applications for a new compression algorithm, based on the Newton method, which provides for a given tensor the optimal tensor product or so-called best separable approximation for fixed Kronecker rank. In combination with a stable quadrature scheme for the Coulomb interaction, tensor product formats enable an efficient evaluation of Coulomb integrals. This is demonstrated by means of best separable approximations for the electron density and Hartree Potential of small molecules, where individual components of the tensor product can be efficiently represented in a wavelet basis. We present a fairly detailed numerical analysis, which provides the basis for further improvements of this novel approach. Our results suggest a broad range of applications within density fitting schemes, which have been recently successfully applied in quantum chemistry.
Stefan Goedecker - One of the best experts on this subject based on the ideXlab platform.
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Linear scaling electronic structure methods
Reviews of Modern Physics, 1999Co-Authors: Stefan GoedeckerAbstract:Methods exhibiting linear scaling with respect to the size of the system, the so-called O(N) methods, are an essential tool for the calculation of the electronic structure of large systems containing many atoms. They are based on algorithms that take advantage of the decay properties of the density matrix. In this article the physical decay properties of the density matrix will first be studied for both metals and insulators. Several strategies for constructing O(N) algorithms will then be presented and critically examined. Some issues that are relevant only for self-consistent O(N) methods, such as the calculation of the Hartree Potential and mixing issues, will also be discussed. Finally some typical applications of O(N) methods are briefly described.
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Electronic Structure Methods Exhibiting Linear Scaling of the Computational Effort with Respect to the Size of the System
arXiv: Condensed Matter, 1998Co-Authors: Stefan GoedeckerAbstract:Methods exhibiting linear scaling with respect to the size of the system, so called O(N) methods, are an essential tool for the calculation of the electronic structure of large systems containing many atoms. They are based on algorithms which take advantage of the decay properties of the density matrix. In this article the physical decay properties of the density matrix will therefore first be studied for both metals and insulators. Several approaches to construct O(N) algorithms will then be presented and critically examined under various aspects. Finally some issues which are relevant only for self-consistent O(N) methods such as the calculation of the Hartree Potential and mixing issues will be discussed.
A. Di Carlo - One of the best experts on this subject based on the ideXlab platform.
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non equilibrium green s functions in density functional tight binding method and applications
New Journal of Physics, 2008Co-Authors: A Pecchia, Gabriele Penazzi, L Salvucci, A. Di CarloAbstract:We present a detailed description of the implementation of the non-equilibrium Green's function (NEGF) technique on the density-functional-based tight-binding (gDFTB) simulation tool. This approach can be used to compute electronic transport in organic and inorganic molecular-scale devices. The DFTB tight-binding formulation gives an efficient computational tool that is able to handle a large number of atoms. NEGFs are used to compute the electronic density self-consistently with the open-boundary conditions naturally encountered in quantum transport problems and the boundary conditions imposed by the Potentials at the contacts. The efficient block-iterative algorithm used to compute the Green's functions is illustrated. The Hartree Potential of the density-functional Hamiltonian is obtained by solving the three-dimensional Poisson equation. A scheme to treat geometrically complex boundary conditions is discussed, including the possibility of including multiterminal calculations.
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Chapter 8 The gDFTB tool for molecular electronics
Theoretical and Computational Chemistry, 2007Co-Authors: Alessandro Pecchia, L. Latessa, Alessio Gagliardi, Th. Frauenheim, A. Di CarloAbstract:Publisher Summary The gDFTB approach for transport computations is based on the density functional tight-binding (DFTB) method, extended to the non-equilibrium Green's functions (NEGF) for the self-consistent computation of charge density and electronic transport. The gDFTB method allows a nearly first-principle treatment of systems comprising a large number of atoms. The Green's function technique enables the computation of the tunneling current flowing between two contacts in a manner consistent with the open boundary conditions that naturally arise in transport problems. The NEGF formalism allows computing the charge density consistently with the non-equilibrium conditions in which a molecular device is driven when biased by an external field. The key ingredient of the self-consistent loop is the solution of the Hartree Potential needed in the density functional Hamiltonian. The Hartree Potential is calculated by solving the three-dimensional Poisson's equation, for the corresponding non-equilibrium charge density computed via the NEGF formalism.
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Tight-Binding DFT for Molecular Electronics (gDFTB)
Introducing Molecular Electronics, 1Co-Authors: A. Di Carlo, Alessandro Pecchia, L. Latessa, Th. Frauenheim, Gotthard SeifertAbstract:We present a detailed description of the implementation of the non-equilibrium Green's function technique on the density-functional-based tight-binding simulation tool (gDFTB). This approach can be used to compute electronic transport in organic and inorganic molecular-scale devices. The tight-binding formulation gives an efficient computational tool able to handle a large number of atoms. The non-equilibrium Green's functions are used to compute the electronic density self-consistently with the open-boundary conditions naturally encountered in transport problems and the boundary conditions imposed by the Potentials at the contacts. The Hartree Potential of the density-functional Hamiltonian is obtained by solving the three-dimensional Poisson's equation involving the non-equilibrium charge density. This method can treat, within a unified framework, coherent and incoherent transport mechanisms.
