A budget way to non-adiabatic molecular dynamics

Trajectory surface hopping combined with time-dependent density functional theory (TD-DFT) is a well established technique to investigate the non-adiabatic dynamics of small to medium sized molecules in the gas phase. Applications to complex materials have been hindered so far by the computational cost. In addition, TD-DFT with conventional functionals suffers from erratic density localization and underestimated charge transfer excitations. Both problems become especially important in large systems.

In this contribution, we summarize recent advances in the development of an approximate TD-DFT scheme (termed TD-DFTB) that allows for excited state simulations of rather large systems. We first present a generalization of the method for the use with range-separated exchange-correlation functionals (LC-DFTB). Its time-dependent extension overcomes the notorious problem of charge-transfer excitations and has recently been combined with the Newton-X software package to perform non-adiabatic molecular dynamics using the fewest switches surface hopping method. Results will be shown for the relaxation dynamics of two cycloparaphenylene molecules, [8]CPP and [10]CPP, explaining the origin of their long fluorescence lifetimes.