Semiclassical wave packet dynamics with electronic structure computed on the fly:: Application to photophysics of electronic excited states in condensed phase

Many semiclassical wave packet propagation methods require only local potential energy surface information in order to update a Gaussian wave packet over a short time interval. These data, which include the evaluation of the potential energy at the instantaneous configuration space center of the wave packet, plus the gradient vector and Hessian (second derivative) matrix at the same configuration, can be generated efficiently by extant electronic structure packages. This leads to an algorithm for propagating semiclassical Gaussian wave packets using electronic structure data computed "on the fly" in the course of the propagation. The feasibility of such a strategy for condensed phase systems is demonstrated by using it (with an appropriate approximate level of electronic structure theory) to calculate Franck-Condon absorption and emission spectra of all-trans 1,3,5,7-octatetraene in the gas phase, and in both chloroform and methanol solvents. Good agreement with the corresponding experimentally measured spectra is obtained.