  The Full Multiple Spawning (FMS) method is designed to simulate quantum
dynamics in the multi-state electronic problem. The FMS nuclear wavefunction is
represented in a basis of coupled, frozen Gaussians, and the spawning procedure
prescribes a means of adaptively increasing the size of the basis in order to
capture population transfer between electronic states. Parent trajectories
create children when passing through regions of significant nonadiabatic
coupling. In order to converge branching ratios without allowing the basis to
reach an impractical size, population transfer at individual spawning events
should be made as effective as possible. Herein we detail a new algorithm for
specifying the initial conditions of freshly spawned basis functions, one that
minimizes the number of spawns needed for convergence by maximizing the
efficiency of individual spawning events. Optimization is achieved by
maximizing the coupling between parent and child trajectories, as a function of
child position and momentum, at the point of spawning. The method is tested
with a two-state, one-mode avoided crossing model and a two-state, two-mode
conical intersection model.

Chemical Physics