Adiabatic dynamics of the solvated electron in liquid ammonia

The adiabatic dynamics of an electron in a polar solvent has been studied by means of a molecular dynamics technique for the coupled electron–solvent system. The method hinges on a separation of time scales for the solvent motion and certain classical dynamical degrees of freedom which represent the ground-state wave function of the electron. For the solvated electron these variables are taken to be the positions and widths of Gaussians that comprise a distributed basis set. The method is applied to an electron in liquid ammonia, and the conditions for the validity of the classical separation of time scales are investigated. Time correlation functions describing the electron diffusion coefficient, and the fluctuation and dissipation of electron energy, are compared with analogous quantities for a classical solute (a chloride ion) in the same solvent. The electron diffusion coefficient in ammonia is calculated to be about twice that of a chloride ion. Experimental mobility data on the electron–ammonia system suggest that the real diffusion coefficient is a factor of 3 larger than calculated for the model used here. Possible reasons for this discrepancy are noted.