The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Julien Toulouse - One of the best experts on this subject based on the ideXlab platform.
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Local Density Approximation for long-range or for short-range energy functionals?
Journal of Molecular Structure: THEOCHEM, 2020Co-Authors: Julien Toulouse, Andreas SavinAbstract:International audienceDensity functional methods were developed, in which the Coulomb electron-electron interaction is split into a long- and a short-range part. In such methods, one term is calculated using traditional Density functional Approximations, like the Local Density Approximation. The present paper tries to shed some light upon the best way to do it by comparing the accuracy of the Local Density Approximation with accurate results for the He atom
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four component relativistic range separated Density functional theory short range exchange Local Density Approximation
Journal of Chemical Physics, 2018Co-Authors: Julien Paquier, Julien ToulouseAbstract:We lay out the extension of range-separated Density-functional theory to a four-component relativistic framework using a Dirac-Coulomb-Breit Hamiltonian in the no-pair Approximation. This formalism combines a wave-function method for the long-range part of the electron-electron interaction with a Density(-current) functional for the short-range part of the interaction. We construct for this formalism a short-range exchange Local-Density Approximation based on calculations on a relativistic homogeneous electron gas with a modified Coulomb-Breit electron-electron interaction. More specifically, we provide the relativistic short-range Coulomb and Breit exchange energies per particle of the relativistic homogeneous electron gas in the form of Pade approximants which are systematically improvable to arbitrary accuracy. These quantities, as well as the associated effective Coulomb-Breit exchange hole, show the important impact of relativity on short-range exchange effects for high densities.We lay out the extension of range-separated Density-functional theory to a four-component relativistic framework using a Dirac-Coulomb-Breit Hamiltonian in the no-pair Approximation. This formalism combines a wave-function method for the long-range part of the electron-electron interaction with a Density(-current) functional for the short-range part of the interaction. We construct for this formalism a short-range exchange Local-Density Approximation based on calculations on a relativistic homogeneous electron gas with a modified Coulomb-Breit electron-electron interaction. More specifically, we provide the relativistic short-range Coulomb and Breit exchange energies per particle of the relativistic homogeneous electron gas in the form of Pade approximants which are systematically improvable to arbitrary accuracy. These quantities, as well as the associated effective Coulomb-Breit exchange hole, show the important impact of relativity on short-range exchange effects for high densities.
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Local Density Approximation for long-range or for short-range energy functionals?
Journal of Molecular Structure: THEOCHEM, 2015Co-Authors: Julien Toulouse, Andreas SavinAbstract:Density functional methods were developed, in which the Coulomb electron-electron interaction is split into a long- and a short-range part. In such methods, one term is calculated using traditional Density functional Approximations, like the Local Density Approximation. The present paper tries to shed some light upon the best way to do it by comparing the accuracy of the Local Density Approximation with accurate results for the He atom.
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Short-range exchange and correlation energy Density functionals: Beyond the Local-Density Approximation
Journal of Chemical Physics, 2015Co-Authors: Julien Toulouse, Francois Colonna, Andreas SavinAbstract:We propose Approximations which go beyond the Local-Density Approximation for the short-range exchange and correlation Density functionals appearing in a multideterminantal extension of the Kohn-Sham scheme. A first Approximation consists of defining Locally the range of the interaction in the correlation functional. Another Approximation, more conventional, is based on a gradient expansion of the short-range exchange-correlation functional. Finally, we also test a short-range generalized-gradient Approximation by extending the Perdew-Burke-Ernzerhof exchange-correlation functional to short-range interactions.
Aurel Bulgac - One of the best experts on this subject based on the ideXlab platform.
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Accuracy of Fission Dynamics Within the Time-dependent Superfluid Local Density Approximation
Acta Physica Polonica B, 2020Co-Authors: J. Grineviciute, Aurel Bulgac, Piotr Magierski, I. StetcuAbstract:We discuss properties of the method based on time dependent superfluid Local Density Approximation (TDSLDA) within an application to induced fission of 240Pu and surrounding nuclei. Various issues related to accuracy of time evolution and the determination of the properties of fission fragments are discussed.
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relativistic coulomb excitation within the time dependent superfluid Local Density Approximation
Physical Review Letters, 2015Co-Authors: I. Stetcu, Aurel Bulgac, Piotr Magierski, C A Bertulani, Kenneth J RocheAbstract:Within the framework of the unrestricted time-dependent Density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus 238U. The approach is based on the superfluid Local Density Approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, the dipole pygmy resonance, and giant quadrupole modes are excited during the process. As a result, the one-body dissipation of collective dipole modes is shown to lead a damping width Γ↓≈0.4 MeV and the number of preequilibrium neutrons emitted has been quantified.
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Time-Dependent Superfluid Local Density Approximation
arXiv: Quantum Gases, 2013Co-Authors: Aurel Bulgac, Michael Mcneil ForbesAbstract:The time-dependent superfluid Local Density Approximation (TDSLDA) is an extension of the Hohenberg-Kohn Density functional theory (DFT) to time-dependent phenomena in superfluid fermionic systems. Unlike linear response theory, which is only valid for weak external fields, the (TDSLDA) approach allows one to study non-linear excitations in fermionic superfluids, including large amplitude collective modes, and the response to strong external probes. Even in the case of weak external fields, the (TDSLDA) approach is technically easier to implement. We will illustrate the implementation of the (TDSLDA) for the unitary Fermi gas, where dimensional arguments and Galilean invariance simplify the form of the functional, and ab initio input from (QMC) simulations fix the coefficients to quite high precision.
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The Asymmetric Superfluid Local Density Approximation (ASLDA)
arXiv: Superconductivity, 2008Co-Authors: Aurel Bulgac, Michael Mcneil ForbesAbstract:Here we describe the form of the Asymmetric Superfluid Local Density Approximation (ASLDA), a Density Functional Theory (DFT) used to model the two-component unitary Fermi gas. We give the rational behind the functional, and describe explicitly how we determine the form of the DFT from the to the available numerical and experimental data.
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superfluid lda slda Local Density Approximation for systems with superfluid correlations
arXiv: Nuclear Theory, 2003Co-Authors: Aurel Bulgac, Yongle YuAbstract:We present a concise account of our development of the first genuine Local Density Approximation (LDA) to the Energy Density Functional (EDF) for fermionic systems with superfluid correlations, with a particular emphasis to nuclear systems.
Andreas Savin - One of the best experts on this subject based on the ideXlab platform.
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Local Density Approximation for long-range or for short-range energy functionals?
Journal of Molecular Structure: THEOCHEM, 2020Co-Authors: Julien Toulouse, Andreas SavinAbstract:International audienceDensity functional methods were developed, in which the Coulomb electron-electron interaction is split into a long- and a short-range part. In such methods, one term is calculated using traditional Density functional Approximations, like the Local Density Approximation. The present paper tries to shed some light upon the best way to do it by comparing the accuracy of the Local Density Approximation with accurate results for the He atom
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Local Density Approximation for long-range or for short-range energy functionals?
Journal of Molecular Structure: THEOCHEM, 2015Co-Authors: Julien Toulouse, Andreas SavinAbstract:Density functional methods were developed, in which the Coulomb electron-electron interaction is split into a long- and a short-range part. In such methods, one term is calculated using traditional Density functional Approximations, like the Local Density Approximation. The present paper tries to shed some light upon the best way to do it by comparing the accuracy of the Local Density Approximation with accurate results for the He atom.
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Short-range exchange and correlation energy Density functionals: Beyond the Local-Density Approximation
Journal of Chemical Physics, 2015Co-Authors: Julien Toulouse, Francois Colonna, Andreas SavinAbstract:We propose Approximations which go beyond the Local-Density Approximation for the short-range exchange and correlation Density functionals appearing in a multideterminantal extension of the Kohn-Sham scheme. A first Approximation consists of defining Locally the range of the interaction in the correlation functional. Another Approximation, more conventional, is based on a gradient expansion of the short-range exchange-correlation functional. Finally, we also test a short-range generalized-gradient Approximation by extending the Perdew-Burke-Ernzerhof exchange-correlation functional to short-range interactions.
G F Bertsch - One of the best experts on this subject based on the ideXlab platform.
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application of the time dependent Local Density Approximation to optical activity
Physical Review A, 1999Co-Authors: Kazuhiro Yabana, G F BertschAbstract:As part of a general study of the time-dependent Local Density Approximation (TDLDA), we here report calculations of optical activity of chiral molecules. The theory automatically satisfies sum rules and the Kramers-Kronig relation between circular dichroism and optical rotatory power. We find that the theory describes the measured circular dichroism of the lowest states in methyloxirane with an accuracy of about a factor of two. In the chiral fullerene C_76 the TDLDA provides a consistent description of the optical absorption spectrum, the circular dichroism spectrum, and the optical rotatory power, except for an overall shift of the theoretical spectrum.
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time dependent Local Density Approximation in real time application to conjugated molecules
International Journal of Quantum Chemistry, 1999Co-Authors: Kazuhiro Yabana, G F BertschAbstract:The time-dependent Local-Density Approximation (TDLDA) is applied to the optical response of conjugated carbon molecules in the energy range of 0--30 eV, with calculations given for carbon chains, polyenes, retinal, benzene, and C{sub 60}. The major feature of the spectra, the collective {pi}-{pi}{sup *} transition, is seen at energies ranging from below 2 to 7 eV and is reproduced by the theory to a few tenths of an electron volt with a good account of systematic trends. However, there is some indication that TDLDA predicts too much fragmentation of the strength function in large molecules. Transition strengths are reproduced with a typical accuracy of 20%. The theory also predicts a broad absorption peak in the range of 15--25 eV, and this feature agrees with experiment in the one case where quantitative data is available (benzene).
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The time-dependent Local Density Approximation for collective excitations of atomic clusters
arXiv: Atomic and Molecular Clusters, 1997Co-Authors: G F Bertsch, Kazuhiro YabanaAbstract:We discuss the calculation of collective excitations in atomic clusters using the time-dependent Local Density Approximation. In principle there are many formulations of the TDLDA, but we have found that a particularly efficient method for large clusters is to use a coordinate space mesh and the algorithms for the operators and the evolution equations that had been developed for the nuclear time-dependent Hartree-Fock theory. The TDLDA works remarkably well to describe the strong excitations in alkali metal clusters and in carbon clusters. We show as an example the benzene molecule, which has two strong features in its spectrum. The systematics of the linear carbon chains is well reproduced, and may be understood in rather simple terms.
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time dependent Local Density Approximation in real time
Physical Review B, 1996Co-Authors: Kazuhiro Yabana, G F BertschAbstract:We study the dipole response of atomic clusters by solving the equations of the time-dependent Local-Density Approximation in real time. The method appears to be more efficient than matrix or Green's function methods for large clusters modeled with realistic ionic pseudopotentials. As applications of the method, we exhibit results for sodium and lithium clusters and for ${\mathrm{C}}_{60}$ molecules. The calculated Mie resonance in ${\mathrm{Na}}_{147}$ is practically identical to that obtained in the jellium Approximation, leaving the origin of the redshift unresolved. The pseudopotential effects are strong in lithium and act to broaden the Mie resonance and give it a substantial redshift, confirming earlier studies. There is also a large broadening due to Landau damping in the calculated ${\mathrm{C}}_{60}$ response, again confirming earlier studies. \textcopyright{} 1996 The American Physical Society.
Kazuhiro Yabana - One of the best experts on this subject based on the ideXlab platform.
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application of the time dependent Local Density Approximation to optical activity
Physical Review A, 1999Co-Authors: Kazuhiro Yabana, G F BertschAbstract:As part of a general study of the time-dependent Local Density Approximation (TDLDA), we here report calculations of optical activity of chiral molecules. The theory automatically satisfies sum rules and the Kramers-Kronig relation between circular dichroism and optical rotatory power. We find that the theory describes the measured circular dichroism of the lowest states in methyloxirane with an accuracy of about a factor of two. In the chiral fullerene C_76 the TDLDA provides a consistent description of the optical absorption spectrum, the circular dichroism spectrum, and the optical rotatory power, except for an overall shift of the theoretical spectrum.
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time dependent Local Density Approximation in real time application to conjugated molecules
International Journal of Quantum Chemistry, 1999Co-Authors: Kazuhiro Yabana, G F BertschAbstract:The time-dependent Local-Density Approximation (TDLDA) is applied to the optical response of conjugated carbon molecules in the energy range of 0--30 eV, with calculations given for carbon chains, polyenes, retinal, benzene, and C{sub 60}. The major feature of the spectra, the collective {pi}-{pi}{sup *} transition, is seen at energies ranging from below 2 to 7 eV and is reproduced by the theory to a few tenths of an electron volt with a good account of systematic trends. However, there is some indication that TDLDA predicts too much fragmentation of the strength function in large molecules. Transition strengths are reproduced with a typical accuracy of 20%. The theory also predicts a broad absorption peak in the range of 15--25 eV, and this feature agrees with experiment in the one case where quantitative data is available (benzene).
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Application of the time-dependent Local-Density Approximation to conjugated molecules
arXiv: Atomic and Molecular Clusters, 1998Co-Authors: Kazuhiro Yabana, George F. BertschAbstract:The time-dependent Local-Density Approximation (TDLDA) is applied to the optical response of conjugated carbon molecules in the energy range of 0-30 eV, with calculations given for carbon chains, polyenes, retinal, benzene and C_60. The major feature of the spectra, the collective pi-pi* transition, is seen at energies ranging from below 2 to 7 eV, and is reproduced by the theory to a few tenths of an eV with a good account of systematic trends. However, there is some indication that TDLDA predicts too much fragmentation of the strength function in large molecules. Transition strengths are reproduced with a typical accuracy of 20%. The theory also predicts a broad absorption peak in the range 15-25 eV, and this feature agrees with experiment in the one case where quantitative data is available (benzene).
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TIME-DEPENDENT Local Density Approximation FOR CLUSTER-ION COLLISIONS
Czechoslovak Journal of Physics, 1998Co-Authors: Piotr Bozek, Kazuhiro YabanaAbstract:The time-dependent Local Density Approximation, which has been successful for collective excitations of atomic clusters in linear response regime, is applied to collision processes where the time-dependent field is given by the Coulomb field of the incoming ions. Preliminary results are discussed on multi-electron transfer processes, i.e., ionizations of metallic clusters.
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The time-dependent Local Density Approximation for collective excitations of atomic clusters
arXiv: Atomic and Molecular Clusters, 1997Co-Authors: G F Bertsch, Kazuhiro YabanaAbstract:We discuss the calculation of collective excitations in atomic clusters using the time-dependent Local Density Approximation. In principle there are many formulations of the TDLDA, but we have found that a particularly efficient method for large clusters is to use a coordinate space mesh and the algorithms for the operators and the evolution equations that had been developed for the nuclear time-dependent Hartree-Fock theory. The TDLDA works remarkably well to describe the strong excitations in alkali metal clusters and in carbon clusters. We show as an example the benzene molecule, which has two strong features in its spectrum. The systematics of the linear carbon chains is well reproduced, and may be understood in rather simple terms.
