Delayed photoisomerisation of the trans-PSB3 retinal toy model using on-the-fly quantum dynamics

Abstract

We explore the trans-cis photoisomerisation process in a representative retinal protonated Schiff base known as trans-PSB3, employing the quantum dynamics method direct dynamics variational multiconfigurational gaussian -- DD-vMCG -- in full dimensionality, i.e., 36 degrees of freedom on potential energy surfaces computed on-the-fly using the SA(2)-CAS(6,6)SCF electronic structure method with the 6-31G basis set. Although the toy molecule has been extensively studied using trajectory methods such as Tully Surface Hopping and Ab Initio Multiple Spawning, the on-the-fly quantum dynamics method DD-vMCG shows a trans-cis isomerisation hundreds of femtoseconds slower using the same electronic structure method, which can be explained in terms of the accesibility to the conical intersection connecting the ground and the excited state.