MOLECULAR-DYNAMICS STUDY OF DIELECTRIC FRICTION

A molecular dynamics study of the friction experienced by the dye mole cule resorufamine rotating in a polar solvent is performed. The validi ty of simple continuum theories of dielectric friction is tested. It i s found that the Alavi-Waldeck theory gives reasonable results for the zero frequency dielectric friction coefficient while the Nee-Zwanzig theory requires an unphysically small cavity radius. A procedure for e valuating the time dependent friction kernel from torques and angular velocities, which enables the contributions to the friction from the v an der Waals and Coulomb forces to be evaluated separately, is suggest ed. This study of a realistic system shows that electrostatic interact ions can enhance friction by at least two physical mechanisms. First i s a contribution to the friction which arises solely from retardation of the solvent reaction field. Second is a contribution arising from l ocal structural changes of the solvent which are driven by the electro static field, i.e., a change in the local viscosity. (C) 1996 American Institute of Physics.