A time-dependent density-functional approach to nonadiabatic electron-nucleus dynamics: formulation and photochemical application

To study nonadiabatic dynamics of the electrons and nuclei, the quantum chemical wavefunction methods have often been invoked to compute the nonadiabatic couplings (NACs), but time-dependent density functional theory (TD-DFT) can provide a formally exact alternative approach when the ground and one excited electronic states are concerned. Based on the density response scheme to compute the NAC vectors [J. Chem. Phys., 2007, 127, 064103], herein presented are a full quantum wave packet and a semi-classical surface hopping approach to the nonadiabatic chemical reactions for the electronically ground and excited states. The adiabatic local density approximation (ALDA) was used here but, contrary to previous simulations based on DFT or TD-DFT, no further approximations were made for the electrons. With those approaches we could successfully describe the photochemical syn-anti isomerization dynamics of a formaldimine molecule (CH2=NH) and investigate the dissipation effects with use of a Langevin dynamics scheme. These simulations demonstrated an important role played by the dissipation and suggested that accurately modeling the dissipation is the next step towards a truly ab initio prediction.