Nonadiabatic dynamics around a conical intersection between electronic states of the same symmetry studied with the thawed Gaussian Ehrenfest dynamics

We present a combination of the Ehrenfest dynamics with the thawed Gaussian wavepacket dynamics. The resulting "thawed Gaussian Ehrenfest dynamics" preserves the molecular energy exactly and partially includes both nuclear quantum and electronically nonadiabatic effects. First, we show that the failure of single-trajectory mean-field methods applied to realistic models of molecules can be explained by the coupled electronic states usually having different symmetry. From this observation, we conclude that our method can be useful to study nonadiabatic dynamics close to conical intersection of electronic states of the same symmetry, which have been understudied due to the difficulty to locate them. Using a diabatic model to simulate such situation, we compare the dynamics of our method with the exact result. We find that the approximate solution provides a good qualitative picture for the first 100 femtoseconds, which include two passages across the conical intersection.