Toward a Correct\nDescription of Initial Electronic\nCoherence in Nonadiabatic Dynamics Simulations

The recent improvement in experimental capabilities for\ninterrogating\nand controlling molecular systems with ultrafast coherent light sources\ncalls for the development of theoretical approaches that can accurately\nand efficiently treat electronic coherence. However, the most popular\nand practical nonadiabatic molecular dynamics techniques, Tully’s\nfewest-switches surface hopping and Ehrenfest mean-field dynamics,\nare unable to describe the dynamics proceeding from an initial electronic\ncoherence. While such issues are not encountered with the analogous\ncoupled-trajectory algorithms or numerically exact quantum dynamics\nmethods, applying such techniques necessarily comes with a higher\ncomputational cost. Here we show that a correct description of initial\nelectronic coherence can indeed be achieved using independent-trajectory\nmethods derived from the semiclassical mapping formalism. The key\nis the introduction of an initial sampling over the electronic phase\nspace and a means of incorporating phase interference between trajectories,\nboth of which are naturally achieved when working within the semiclassical\nmapping framework.