Search results for "Green's function"
showing 10 items of 35 documents
Levels of self-consistency in the GW approximation
2009
We perform $GW$ calculations on atoms and diatomic molecules at different levels of self-consistency and investigate the effects of self-consistency on total energies, ionization potentials and on particle number conservation. We further propose a partially self-consistent $GW$ scheme in which we keep the correlation part of the self-energy fixed within the self-consistency cycle. This approximation is compared to the fully self-consistent $GW$ results and to the $G W_0$ and the $G_0W_0$ approximations. Total energies, ionization potentials and two-electron removal energies obtained with our partially self-consistent $GW$ approximation are in excellent agreement with fully self-consistent $…
Nonequilibrium Green's function approach to strongly correlated few-electron quantum dots
2009
The effect of electron-electron scattering on the equilibrium properties of few-electron quantum dots is investigated by means of nonequilibrium Green's function theory. The ground and equilibrium states are self-consistently computed from the Matsubara (imaginary time) Green's function for the spatially inhomogeneous quantum dot system whose constituent charge carriers are treated as spin-polarized. To include correlations, the Dyson equation is solved, starting from a Hartree-Fock reference state, within a conserving (second-order) self-energy approximation where direct and exchange contributions to the electron-electron interaction are included on the same footing. We present results for…
Efficient and accurate computation of Green's function for the Poisson equation in rectangular waveguides
2009
[1] In this paper, a new algorithm for the fast and precise computation of Green's function for the 2-D Poisson equation in rectangular waveguides is presented. For this purpose, Green's function is written in terms of Jacobian elliptic functions involving complex arguments. A new algorithm for the fast and accurate evaluation of such Green's function is detailed. The main benefit of this algorithm is successfully shown within the frame of the Boundary Integral Resonant Mode Expansion method, where a substantial reduction of the computational effort related to the evaluation of the cited Green's function is obtained.
Polymer-metal plasmonic waveguide : passive and active components for integrated photonics
2009
Dielectric loaded surface plasmon polariton waveguides (DLSPPWs) enable transmission at a sub-wavelength scale of both electrical and plasmonic (optical waves at the interface between a metal and a dielectric) signals in the same circuitry. Moreover, the use of a polymer as the dielectric load enables the functionalization of DLSPPWs. Therefore, this configuration is of great interest for integrated photonic applications. However, DLSPPWs suffer strong losses due to dissipation into the metal film. We address here the possibility of compensating the losses using a configuration analogous to an optical amplifier. We first set theoretical (effective index model), numerical (differential metho…
Ab-initio Calculation of the Properties of Permalloys Used in Electrical Machines
2006
In this paper an ab-initio calculation that allows to describe the main features of permalloys is presented. The calculation is bawd on Korringa-Kohn-Rostoker electronic structure method. The dependence of the magnetocryttalline anisotropy and of the magnetostriction on the concentration of non magnetic addiction is computed.
The generalized Kadanoff-Baym ansatz with initial correlations
2018
Within the non-equilibrium Green's function (NEGF) formalism, the Generalized Kadanoff-Baym Ansatz (GKBA) has stood out as a computationally cheap method to investigate the dynamics of interacting quantum systems driven out of equilibrium. Current implementations of the NEGF--GKBA, however, suffer from a drawback: real-time simulations require {\em noncorrelated} states as initial states. Consequently, initial correlations must be built up through an adiabatic switching of the interaction before turning on any external field, a procedure that can be numerically highly expensive. In this work, we extend the NEGF--GKBA to allow for {\em correlated} states as initial states. Our scheme makes i…
On Green's function for cylindrically symmetric fields of polarized radiation
2009
Analytic expressions for Green's function describing the process of transfer of polarized radiation in homogeneous isotropic infinite medium in case of cylindrical symmetry and nonconservative scattering are obtained. The solution is based on the set of systems of Abel integral equations of the first kind obtained using the principle of superposition, and the known expression of Green's function for radiation fields with plane-parallel symmetry. Eigenvalue decompositions for the corresponding matrices of generalized spherical functions are found. Using this result the systems of Abel integral equations are diagonalized, and the final solution is obtained.
On Green's function for spherically symmetric problems of transfer of polarized radiation
2005
Analytic expressions for Green's function describing the process of transfer of polarized radiation in homogeneous isotropic infinite medium in case of spherical symmetry and nonconservative scattering are obtained. Spherical eigenfunctions of the homogeneous transfer equation are not used, due to their strong divergence; instead, direct transformation from plane-parallel to spherical symmetry is carried out, leading to convergent solutions. The possible existence of generalized eigenfunctions of homogeneous transfer equation is accounted for.
Effective bias and potentials in steady-state quantum transport: A NEGF reverse-engineering study
2016
Using non-equilibrium Green’s functions combined with many-body perturbation theory, we have calculated steady-state densities and currents through short interacting chains subject to a finite electric bias. By using a steady-state reverse-engineering procedure, the effective potential and bias which reproduce such densities and currents in a non-interacting system have been determined. The role of the effective bias is characterised with the aid of the so-called exchange-correlation bias, recently introduced in a steady-state density-functionaltheory formulation for partitioned systems. We find that the effective bias (or, equivalently, the exchange-correlation bias) depends strongly on th…
One-particle Green's function
2013
In this chapter we get acquainted with the one-particle Green's function G , or simply the Green's function. The chapter is divided in three parts. In the first part (Section 6.1) we illustrate what kind of physical information can be extracted from the different Keldysh components of G . The aim of this first part is to introduce some general concepts without being too formal. In the second part (Section 6.2) we calculate the noninteracting Green's function. Finally in the third part (Sections 6.3 and 6.4) we consider the interacting Green's function and derive several exact properties. We also discuss other physical (and measurable) quantities that can be calculated from G and that are re…