Theory of the Molecular Friction Constant

Abstract

The molecular friction tensor, as given by a time integral of an autocorrelation of forces, is calculated with the assumption that the trajectories of the particles are linear and unaccelerated for the times of interest. Such trajectories are appropriate to lowest order in the force on a particle. Application is made to particles interacting via a Coulombic potential. The result previously derived by Chandrasekhar is obtained without the introduction of a cutoff for large distances. In order to handle molecular systems we treat the ``soft'' part of the potential by the linear trajectory technique, and add a small term to account for hard-core collisions.