The transient response function of the density profile of the solvent around a solute during the translational diffusion of the solute was formulated based on the generalized Langevin formalism. The resultant theory was applied to both neet Lennard-Jones fluids and cations in liquid water, and the response functions were obtained from the analysis of the molecular dynamics simulations. In the case of the self-diffusion of Lennard-Jones fluids, the responses of the solvation structures were in harmony with conventional pictures based on the mode-coupling theory, that is, the binary collision in the low-density fluids, the backflow effect from medium to high density fluids, and the backscatter effect in the liquids near the triple point. In the case of cations in water, the qualitative behavior was strongly dependent on the size of cations. The pictures similar to simple dense liquids were obtained for the large ion and the neutral molecule, while the solvent waters within the first solvation shell of small ions exhibited an oscillatory response in the short-time region. In particular, the oscillation was remarkably underdamped for lithium ion. The origin of the oscillation was considered with regard to the theoretical treatment of the translational diffusion of ions in water.

Molecular Dynamics Simulation Study on the Transient Response of Solvation Structure during the Translational Diffusion of Solute. Yamaguchi, T., Matsuoka, T., Koda, S.: Journal of Chemical Physics, 2005, 122[1], 014512