Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 49: Ab-initio approaches to excitations in condensed matter II
O 49.10: Vortrag
Donnerstag, 26. März 2009, 12:45–13:00, SCH 251
The multiconfigurational time-dependent Hartree-Fock method for excited states: Theory and application to conjugated polymers — •Rafael P. Miranda1, Andrew P. Horsfield2, and Andrew J. Fisher1 — 1Department of Physics and Astronomy, University College London, London, United Kingdom — 2Department of Materials, Imperial College London, London, United Kingdom
The solution of the time-dependent Schrödinger equation for systems of interacting electrons is generally a prohibitive task, for which approximate methods are highly desirable. One of the simplest schemes, known as the time-dependent Hartree-Fock (TDHF) approximation, consists in restricting the electronic wavefunction to a single Slater determinant. However, several physical processes of interest involve excited states which can not be properly described by a single determinant. For instance, in a photoexcitation process, absorption of a photon creates an open-shell singlet state, and thus devising a scheme which retains the proper spin symmetry requires two Slater determinants. In this work, we extend the TDHF method to such multiconfigurational states. Based on a time-dependent variational principle, we derive the optimal equations of motion for the single-particle molecular orbitals. This method, together with a classical description of the ionic degrees of freedom (mean-field approximation), is then applied to study the dynamics of photoexcitations in conjugated polymers. We show the relaxation of electron-hole pairs to form excitons and charged polarons, and discuss the modifications to the relaxation process predicted by the inclusion of the Coulomb interaction between the carriers.