19 research outputs found
Optical absorption spectra of finite systems from a conserving Bethe-Salpeter equation approach
We present a method for computing optical absorption spectra by means of a
Bethe-Salpeter equation approach, which is based on a conserving linear
response calculation for electron-hole coherences in the presence of an
external electromagnetic field. This procedure allows, in principle, for the
determination of the electron-hole correlation function self-consistently with
the corresponding single-particle Green function. We analyze the general
approach for a "one-shot" calculation of the photoabsorption cross section of
finite systems, and discuss the importance of scattering and dephasing
contributions in this approach. We apply the method to the closed-shell
clusters Na_4, Na^+_9 and Na^+_(21), treating one active electron per Na atom.Comment: 9 pages, 3 figure
The Role of Bound States in Time-Dependent Quantum Transport
Charge transport through a nanoscale junction coupled to two macroscopic
electrodes is investigated for the situation when bound states are present. We
provide numerical evidence that bound states give rise to persistent,
non-decaying current oscillations in the junction. We also show that the
amplitude of these oscillations can exhibit a strong dependence on the history
of the applied potential as well as on the initial equilibrium configuration.
Our simulations allow for a quantitative investigation of several transient
features. We also discuss the existence of different time-scales and address
their microscopic origin.Comment: 10 pages, 8 figure
Double ionization of a two-electron system in the time- dependent extended Hartree-Fock approximation
Double ionization of a two-electron system in the time- dependent extended Hartree-Fock approximation
Conserving approximations in nonequilibrium Green function and density functional theory
Fully self-consistent GW calculations for atoms and molecules
We solve the Dyson equation for atoms and diatomic molecules within the GW approximation, in order to elucidate the effects of self-consistency on the total energies and ionization potentials. We find GW to produce accurate energy differences although the self-consistent total energies differ significantly from the exact values. Total energies obtained from the Luttinger-Ward functional ELW[G] with simple, approximate Green functions as input, are shown to be in excellent agreement with the self-consistent results. This demonstrates that the Luttinger-Ward functional is a reliable method for testing the merits of different self-energy approximations without the need to solve the Dyson equation self-consistently. Self-consistent GW ionization potentials are calculated from the Extended Koopmans Theorem, and shown to be in good agreement with the experimental results. We also find the self-consistent ionization potentials to be often better than the non-self-consistent G0W0 values. We conclude that GW calculations should be done self-consistently in order to obtain physically meaningful and unambiguous energy differences.