Density Functional Tight Binding Calculations for Probing Electronic-Excited States of Large Systems

This review focuses on the application of Density Functional Tight Binding (DFTB) to electronic-excited states, which has attracted significant attention for extending the computationally efficient approach to the time domain. The chapter highlights the use of real-time time-dependent-DFTB to probe the electron dynamics of large systems in external electric fields where the nuclei are held fixed. Surface hopping is a general mixed quantum-classical nonadiabatic dynamics methodology with many variants, such as fewest-switches surface-hopping, decoherence induced surface hopping, independent electron surface hopping, and others. The nuclei are propagated according to classical mechanics, and the forces on the nuclei, at any given instant of time, arise from a single adiabatic potential energy surfaces. The review illustrates the charge transfer dynamics of Phenyl-C61-butyric acid methyl ester/polythiophene, which is a model system for understanding photo-induced charge transfer dynamics in organic photovoltaics.