Regensburg 2013 – scientific programme
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O: Fachverband Oberflächenphysik
O 21: Electronic Structure and Spin-Orbit Interaction I
O 21.4: Talk
Monday, March 11, 2013, 16:45–17:00, H42
Accurate calculation of optical excitations for large systems — •Margherita Marsili1 and Paolo Umari1,2 — 1Dipartimento di Fisica e Astronomia, Universitá di Padova, via Marzolo 8, I-35131 Padova, Italy — 2CNR-IOM, Theory@Elettra group, Trieste, Italy
Many-body perturbation theory is the natural framework for the description of electronic excited state properties. For instance, within MBPT, single-particle excitation energies (as probed by photoemission and STS experiments) are found at the poles of the single particle Green’s function. Response functions, describing optical spectra, are calculated via the solution of the Bethe-Salpeter equation (BSE), which explicitly contains the electron-hole interaction.When excitonic effects are neglected, absorption spectra are often in bad agreement with the experiments. The agreement with experiment is restored when the electron-hole interactions are included. Excited states are in this case described as linear combinations of independent-particle transition. Although very accurate, the appealing of the BSE scheme is limited due to its high computational cost. We will show how we can enlarge the scope of BSE calculations. First, we the use maximally localized Wannier’s functions for reducing strongly the terms which need to to be calculated for evaluating the electron-hole interaction Then, we avoid any explicit sum over empty one-particle orbitals. As a consequence we are able to determine, not only the excitation spectra, but also, directly, each excited state. We validate our scheme by addressing the optical excitations of small isolated molecules. Finally, we will illustrate a few examples where larger systems are investigated.