The Experts below are selected from a list of 26526 Experts worldwide ranked by ideXlab platform
Taisuke Ozaki - One of the best experts on this subject based on the ideXlab platform.
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efficient implementation of the nonequilibrium green function method for electronic transport calculations
2010Co-Authors: Taisuke Ozaki, Kengo Nishio, Hiori KinoAbstract:An efficient implementation of the nonequilibrium Green function method combined with the density-Functional theory, using localized pseudoatomic orbitals, is presented for electronic transport calculations of a system connected with two leads under a finite bias voltage. In the implementation, accurate and efficient methods are developed especially for the evaluation of the density matrix and treatment of boundaries between the scattering region and the leads. Equilibrium and nonequilibrium contributions in the density matrix are evaluated with very high precision by a contour integration with a continued fraction representation of the Fermi-Dirac function and by a simple quadrature on the real axis with a small imaginary part, respectively. The Hartree potential is computed efficiently by a combination of the two-dimensional fast Fourier transform and a finite difference method, and the charge density near the boundaries is constructed with a careful treatment to avoid the spurious scattering at the boundaries. The efficiency of the implementation is demonstrated by rapid convergence properties of the density matrix. In addition, as an illustration, our method is applied for zigzag graphene nanoribbons, a Fe/MgO/Fe tunneling junction, and a ${\text{LaMnO}}_{3}/{\text{SrMnO}}_{3}$ superlattice, demonstrating its applicability to a wide variety of systems.
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continued fraction representation of the fermi Dirac function for large scale electronic structure calculations
2007Co-Authors: Taisuke OzakiAbstract:An efficient and accurate contour integration method is presented for large-scale electronic structure calculations based on the Green function. By introducing a continued fraction representation of the Fermi-Dirac function derived from a hypergeometric function, the Matsubara summation is generalized with respect to distribution of poles so that the integration of the Green function can converge rapidly. Numerical illustrations, evaluation of the density matrix for a simple model Green function and a total energy calculation for aluminum bulk within density functional theory, clearly show that the method provides remarkable convergence with a small number of poles, indicating that the method can be applied to not only the electronic structure calculations, but also a wide variety of problems.
F Strafella - One of the best experts on this subject based on the ideXlab platform.
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system of self gravitating semidegenerate fermions with a cutoff of energy and angular momentum in their distribution function
1992Co-Authors: G Ingrosso, Marco Merafina, Remo Ruffini, F StrafellaAbstract:The gravitational equilibrium of static, spherically symmetric, Newtonian systems consisting of a collisionless semidegenerate Fermi gas is studied. A cutoff in the phase space distribution function of the particles is introduced in order to avoid the problems arising from the infinite radius of semi-degenerate configurations when the usual Fermi-Dirac function is used. Here, the more general case of a cutoff in energy and angular momentum is considered, the latter giving an anisotropy in the velocity space
Hiori Kino - One of the best experts on this subject based on the ideXlab platform.
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efficient implementation of the nonequilibrium green function method for electronic transport calculations
2010Co-Authors: Taisuke Ozaki, Kengo Nishio, Hiori KinoAbstract:An efficient implementation of the nonequilibrium Green function method combined with the density-Functional theory, using localized pseudoatomic orbitals, is presented for electronic transport calculations of a system connected with two leads under a finite bias voltage. In the implementation, accurate and efficient methods are developed especially for the evaluation of the density matrix and treatment of boundaries between the scattering region and the leads. Equilibrium and nonequilibrium contributions in the density matrix are evaluated with very high precision by a contour integration with a continued fraction representation of the Fermi-Dirac function and by a simple quadrature on the real axis with a small imaginary part, respectively. The Hartree potential is computed efficiently by a combination of the two-dimensional fast Fourier transform and a finite difference method, and the charge density near the boundaries is constructed with a careful treatment to avoid the spurious scattering at the boundaries. The efficiency of the implementation is demonstrated by rapid convergence properties of the density matrix. In addition, as an illustration, our method is applied for zigzag graphene nanoribbons, a Fe/MgO/Fe tunneling junction, and a ${\text{LaMnO}}_{3}/{\text{SrMnO}}_{3}$ superlattice, demonstrating its applicability to a wide variety of systems.
G Ingrosso - One of the best experts on this subject based on the ideXlab platform.
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system of self gravitating semidegenerate fermions with a cutoff of energy and angular momentum in their distribution function
1992Co-Authors: G Ingrosso, Marco Merafina, Remo Ruffini, F StrafellaAbstract:The gravitational equilibrium of static, spherically symmetric, Newtonian systems consisting of a collisionless semidegenerate Fermi gas is studied. A cutoff in the phase space distribution function of the particles is introduced in order to avoid the problems arising from the infinite radius of semi-degenerate configurations when the usual Fermi-Dirac function is used. Here, the more general case of a cutoff in energy and angular momentum is considered, the latter giving an anisotropy in the velocity space
Remo Ruffini - One of the best experts on this subject based on the ideXlab platform.
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system of self gravitating semidegenerate fermions with a cutoff of energy and angular momentum in their distribution function
1992Co-Authors: G Ingrosso, Marco Merafina, Remo Ruffini, F StrafellaAbstract:The gravitational equilibrium of static, spherically symmetric, Newtonian systems consisting of a collisionless semidegenerate Fermi gas is studied. A cutoff in the phase space distribution function of the particles is introduced in order to avoid the problems arising from the infinite radius of semi-degenerate configurations when the usual Fermi-Dirac function is used. Here, the more general case of a cutoff in energy and angular momentum is considered, the latter giving an anisotropy in the velocity space