DYNAMIC EFFECTS OF IONS ON A POLAR-SOLVENT

The dynamical behavior of ion pairs in a polar diatomic solvent is investigated by using molecular dynamics (MD) computer simulations. Two methods are employed. One is a full-scale MD calculation without approximations, while the other uses the clamping approximation (CA). A comparison of the results from these two methods gives information about the dynamical effects. For example, it is found that for LiF the cation attracts more solvent molecules than the anion does. This effect is enhanced by the mass difference of Li and F on the dynamics. This result is in line with experimental observations. The relaxation features of the rotational and translational motions of the neighboring solvent molecules are quite different. The former exhibits a high-frequency oscillation induced by the high-frequency intramolecular vibrations of the ion pair, while the latter decays as a damped oscillator with a much lower frequency. A nonexponential response of the molecular reorientation of the polar solvent is observed. © 1990 American Chemical Society.