Electronically excited processes occur in many systems of interest, such as photosynthetic light harvesting, fluorescent proteins, UV damage to DNA, and exciton dissociation in organic photovoltaics. Our understanding of these systems can be aided greatly by ab initio excited-state dynamics simulations; however, before such simulations become routine, more work needs to be done to improve excited-state electronic structure methods. In particular, state-averaged multiconfigurational self-consistent field (SA-MCSCF) electronic structure is a workhorse of excited-state dynamics simulations, but the method suffers from known problems that have hampered its wider adoption. One problem arises from the use of state averaging, vital for a proper description of electronic degeneracies, that creates an imbalanced treatment of the electronic states included in the state averaging and those outside it, resulting in potential energy surface discontinuities when these states cross. Presented here is an approach that dynamically adjusts the state weights according to their energetic separation [J. Chem. Phys. <b>141</b>, 171102 (2014)]. Dynamic weighting is seen to smooth out discontinuities in potential energy surfaces while retaining the overall shape of SA-MCSCF curves. Analytical gradients are also derived, enabling excited-state ab initio molecular dynamics and the method is applied to a prototypical cis-trans photoisomerization reaction. Finally, extension of the approach to multireference perturbation theory electronic structure is presented.

Smoothing out excited-state dynamics: Dynamically weighted multiconfigurational self-consistent field

252nd National Meeting (2016)

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