Temperature-dependent self-trapped exciton relaxation in alkali halides: molecular dynamics study

New molecular dynamics (NM) simulations of the relaxation of self-trapped excitons (STE) in NaCl have been performed with a cluster size of 1055 atoms at temperatures in the range 15 K to 300 K. For the first time, significantly different relaxation end products are obtained at a given temperature depending on the choice of the intitial atomic positions and velocities. From 15 K to 65 K, either the STE or a Frenkel defect pair can be found at the end of a few picoseconds. Between 65 K and 150 K only Frenkel defects are found after the same interval. At 250 K and above, STEs and Frenkel defects are again both found as end products after a few picoseconds, presumably as a result of large amplitude atomic motions which hinder the coherent process to be discussed. Within a limited statistical basis, it has been possible to estimate a defect formation rate, which peaks around 100 K. The result is interpreted as an indication of stochastic resonance. (c) 2006 WELEY-VCH Verlag GmbH & Co. KGaA, Weinheim.