Nonadiabatic dynamics with the help of multiconfigurational Ehrenfest method: Improved theory and fully quantum 24D simulation of pyrazine

This article proposes an improved version of recently developed multiconfigurational Ehrenfest approach to quantum dynamics. The idea of the approach is to use frozen Gaussians (FG) guided by Ehrenfest trajectories as a basis set for fully quantum propagation. The method is applied to simulation of nonadiabatic dynamics of pyrazine and shows that nonadiabatic dynamics on two coupled electronic states S-2 and S-1, which determines pyrazine absorption spectrum, can be simulated with the help of a basis comprised of very small number of trajectory guided basis functions. For the 24 dimensional (24D) model, good results were obtained with the basis of only 250 trajectories guided FG per electronic state. The efficiency of the method makes it particularly suitable for future application together with direct dynamics, calculating potentials on the fly. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3442747]