DECOHERENT HISTORIES AND NONADIABATIC QUANTUM MOLECULAR-DYNAMICS SIMULATIONS

The role of quantum coherence loss in mixed quantum-classical dynamica l systems is explored in the context of the theory of quantum decohere nce introduced recently by Bittner and Rossky [J. Chem. Phys. 103, 813 0 (1995)]. This theory, which is based upon the consistent histories i nterpretation of quantum mechanics, introduces decoherence in the quan tum subsystem by carefully considering the relevant time and length sc ales over which one must consider the effects of phase interference be tween alternative histories of the classical subsystem. Such alternati ve histories are an integral part of any quantum-classical computation al scheme which employs transitions between discrete quantum states; c onsequently, the coherences between alternative histories have a profo und effect on the transition probability between quantum states. In th is paper, we review the Bittner-Rossky theory and detail a computation al algorithm suitable for large-scale quantum molecular dynamics simul ations which implements this theory. Application of the algorithm towa rds the relaxation of a photoexcited aqueous electron compare well to previous estimates of the excited state survival time as well as to th e experimental measurements. (C) 1997 American Institute of Physics. [ S0021-9606(97)50944-5].