NONLINEAR EFFECTS OF SOLVATION DYNAMICS

The nonlinear Smoluchowski-Vlasov equation is calculated to investigat e nonlinear effects on solvation dynamics. While a linear response has been assumed for free energy in equilibrium solvent, the equation inc ludes dynamical nonlinear terms. The solvent density function is expan ded in terms of spherical harmonics for orientation of solvent molecul es, and then only terms for l=0 and 1, and m=0 are taken. The calculat ed results agree qualitatively with that obtained by many molecular dy namics simulations. In the long-term region, solvent relaxation for a change from a neutral solute to a charged one is slower than that obta ined by the linearized equation. Further, in the model, the nonlinear terms lessen effects of acceleration by the translational diffusion on solvent relaxation.