29 research outputs found
Solving the Kadanoff-Baym equations for inhomogenous systems: Application to atoms and molecules
We have implemented time-propagation of the non-equilibrium Green function
for atoms and molecules, by solving the Kadanoff-Baym equations within a
conserving self-energy approximation. We here demonstrate the usefulnes of
time-propagation for calculating spectral functions and for describing the
correlated electron dynamics in a non-perturbative electric field. We also
demonstrate the use of time-propagation as a method for calculating
charge-neutral excitation energies, equivalent to highly advanced solutions of
the Bethe-Salpeter equation.Comment: 4 pages, 5 figure
Nonequilibrium Green function theory for excitation and transport in atoms and molecules
In this work we discuss the application of nonequilibrium Green functions theory to atomic and molecular systems with the aim to study charge and energy transport in these systems. We apply the Kadanoff-Baym equations to atoms and diatomic molecules initially in the ground state. The results obtained for the correlated initial states are used to analyze variational energy functionals of the Green function which are shown to perform very well. We further show an application of the Kadanoff-Baym equations to a molecule exposed to an external laser field. Finally we discuss the connection between nonequilibrium Green function theory and time-dependent density-functional theory with the aim to develop better density functionals in order to treat larger systems than those attainable with the nonequilibrium Green function method.</p
Propagating the Kadanoff-Baym equations for atoms and molecules
While the use of Green’s function techniques has a long tradition in quantum chemistry, the possibility of propagating the Kadanoff-Baym equations has remained largely unexplored. We have implemented the time-propagation for atoms and diatomic molecules, starting from a system in the groundstate. The initial stage of the calculation requires solving the Dyson equation self-consistently for the equilibrium Green’s function. This Green’s function contains a huge amount of information, and we have found it particularly interesting to compare the self-consistent total energies to the results of variational energy functionals of the Green’s function. We also use time-propagation for calculating linear response functions, as a means for obtaining the excitation energies of the system. We have presently implemented the propagation for the second Born approximation, while the GW approximation has now been implemented for the ground state calculations
Variational energy functionals of the Green function tested on molecules
It was recently proposed to use variational functionals based on manybody perturbation theory for the calculation of the total energies of many-electron systems. The accuracy of such functionals depends on the degree of sophistication of the underlying perturbation expansions. The energy functionals are variational in the sense that they can be evaluated at rather crude approximations to their independent variables which are the one-electron Green function, or the one-electron Green function and the dynamically screened electron interaction. The functionals were previously applied to the electron gas and shown to be extraordinarily accurate already at the level of the so-called GW approximation (GWA). In the current work we have tested the functional due to Luttinger and Ward, which is a functional of the Green function. Using density functional theory (DFT) and Hartree-Fock Green functions as input variables, we have calculated total energies of diatomic molecules at the level of the GWA as well as with second-order exchange effects included. We will also discuss various other variational energy functionals, including DFT orbital functionals based on many-body perturbation theory. (C) 2004 Wiley Periodicals, Inc
Time-propagation of the Kadanoff-Baym equations for inhomogeneous systems
We have developed a time propagation scheme for the Kadanoff-Baym equations
for general inhomogeneous systems. These equations describe the time evolution
of the nonequilibrium Green function for interacting many-body systems in the
presence of time-dependent external fields. The external fields are treated
nonperturbatively whereas the many-body interactions are incorporated
perturbatively using Phi-derivable self-energy approximations that guarantee
the satisfaction of the macroscopic conservation laws of the system. These
approximations are discussed in detail for the time-dependent Hartree-Fock, the
second Born and the GW approximation.Comment: 8 pages, 2 figure