On the fluctuation-dissipation theorem for interacting brownian particles

Abstract

The correct form of the fluctuation-dissipation theorem for interacting brownian particles contains a term due to the interparticle force, which has usually been ignored in brownian dynamics (BD) simulations. In order to estimate its size, a BD simulation of n-butane has been performed. The term appears to be virtually zero.

Besides, the process of energy transfer through the molecule has been studied. It displays two time scales. Energy relaxation involving the bond length and bond angle degrees of freedom takes less than 1 ps, whereas the energy is only completely redistributed after about 100 ps, which is due to the weak coupling of the atoms through the dihedral degree of freedom.