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O: Fachverband Oberflächenphysik

O 49: Ab-initio approaches to excitations in condensed matter II

O 49.1: Vortrag

Donnerstag, 26. März 2009, 10:30–10:45, SCH 251

Effects of electron-phonon interaction beyond mean-field approximation in the non-adiabatic dynamics of photo-excited short polyacetylene chains — •Lorenzo Stella — London Centre for Nanotechnology, London, United Kingdom — University College London, London, United Kingdom

Conjugated polymers, of which polyacetylene is the simplest example, combine good mechanical and electronic properties that may be exploited in future technological applications. To this end, a proper description of photo-generation of charged and neutral excitations is crucial. In particular, if quantum vibrational modes (phonons) can be excited, the adiabatic approximation is no longer applicable and this will affect the transfer of energy from the electronic excitations. I show here that neglecting quantum fluctuations of atoms can lead to a qualitatively wrong account of the relaxation dynamics of photo-excited short polyacetylene chains. Indeed, even at zero temperature, quantum fluctuations of the molecular degrees of freedom can trigger the decay of an excited electronic state, through spontaneous emission of phonons: within a mean-field approach, such a process cannot be described at all. A proper study of this quantum phenomenon is given here by an improved version of Correlated Electron-Ion Dynamics (CEID) which includes quantum fluctuations of atoms about their mean-field trajectories in a converging perturbative way. This method is stable, efficient and provides a smooth evolution for both electronic and molecular degrees of freedom. Implications of the obtained results on the efficiency of conjugated polymer devices are also discussed.