Mean-Field Molecular Dynamics with Surface Hopping: Application to the Aqueous Solvated Electron

To evaluate the suitability of the combined mean-field/surface hopping (MF/SH) algorithm (Prezhdo, O. V.; Rossky, P. J. J. Chem. Phys. 1997, 107, 825) for the simulation of realistic chemical environments, we have implemented MF/SH for the nonadiabatic molecular dynamics simulation of the aqueous solvated electron. The relaxation dynamics following both electron injection into pure water and photoexcitation from the equilibrium ground-state electron-water system are considered. The validity of a mean-field evolution of the classical variables is monitored via the deviations of the solvent coordinates and momenta between the mean-field molecular dynamics trajectory and a reference adiabatic molecular dynamics trajectory. In agreement with earlier MF/SH simulations on low dimensional model systems, our results show that divergence between momenta occurs rather rapidly. Present results show that mean-field evolution is valid on a 30−70 fs time scale for ground-state excitation and on a 7−10 fs interval for the electron injection environment. Even for the shorter time cases, the times correspond to ∼20 solvent time steps in simulation. Considering that estimated electronic coherence times for excited state dynamics are considerably shorter, the results indicate that the method is a viable one for high dimensional, strongly interacting systems.