NONLINEAR EFFECTS OF NUMBER DENSITY OF SOLVENT MOLECULES ON SOLVATIONDYNAMICS

For the number density of solvent molecules, nonlinear effects on solv ation dynamics are studied using the dynamical density functional meth od. The present method includes nonlinear coupling between the number density and a polarization field only in the free energy functional. B y means of the nonlinear free energy functional, nonlinear differentia l-integral equations are developed for the polarization field and numb er density. Numerical calculations show that solvent molecules relax m ore slowly around an ion than around a neutral solute. This result agr ees qualitatively with nonlinear effects observed in many molecular dy namics simulations. In addition, the nonlinear dynamics of hydrogen bo nds can be understood, by considering the slow relaxation of the numbe r density of solvent molecules. (C) 1996 American Institute of Physics .