Including Photoexcitation\nExplicitly in Trajectory-Based\nNonadiabatic Dynamics at No Cost

Over the last decades,\ntheoretical photochemistry has\nproduced\nmultiple techniques to simulate the nonadiabatic dynamics of molecules.\nSurprisingly, much less effort has been devoted to adequately describing\nthe first step of a photochemical or photophysical process: photoexcitation.\nHere, we propose a formalism to include the effect of a laser pulse\nin trajectory-based nonadiabatic dynamics at the level of the initial\nconditions, with no additional cost. The promoted density approach\n(PDA) decouples the excitation from the nonadiabatic dynamics by defining\na new set of initial conditions, which include an excitation time.\nPDA with surface hopping leads to nonadiabatic dynamics simulations\nin excellent agreement with quantum dynamics using an explicit laser\npulse and highlights the strong impact of a laser pulse on the resulting\nphotodynamics and the limits of the (sudden) vertical excitation.\nCombining PDA with trajectory-based nonadiabatic methods is possible\nfor any arbitrary-sized molecules using a code provided in this work.