Non-adiabatic dynamics using time-dependent density functional theory: Assessing the coupling strengths

Light-driven reactions constitute an important class of processes in physics, chemistry, and biology. The development of accurate and efficient computational tools for the study of excited states dynamics has thus become of primary importance. Recently, we have developed a non-adiabatic ab initio molecular dynamics (AIMD) method, which combines Tully's surface hopping with TDDFT. Here, we investigate some fundamental aspects of this AIMD scheme that deal with the accuracy of TDDFT potential energy surfaces in regions of strong coupling and with the associated intensity of the non-adiabatic couplings (NACs). Of particular interest is the coupling between the ground and the first excited singlet state, which constitute a potential pitfall for all non-adiabatic AIMD based on TDDFT. To this end, we have investigated the excited state dynamics of protonated formaldimine (CH2NH2+) with particular emphasis on the analysis of the NAC strengths in regions of the configurational space close to surface hopping points and conical intersections. A good agreement of the structural and dynamical properties is found with respect to state averaged multiconfiguration self consistent field results.