The fluctuation-dissipation theorem in the itinerant-oscillator model of liquids

Abstract

Attention is called to the following consequence of the fluctuation- dissipation theorem, that the generalized friction constants in the 'generalized Langevin equation', and hence its solution, are uniquely determined in terms of the time-dependent correlation function of random forces and the instantaneous correlation functions of the dynamical variables, provided that the equation is written in a proper form. This fact is applied to the Sears (1965) itinerant-oscillator model of liquids. Under the assumptions which Sears adopted for the random forces and the equilibrium correlations of dynamical variables, the generalized Langevin equation derived is identical to the one given by Damle, Sjolander and Singwi (1968) by adding a reaction term to Nakahara and Takahashi's (1966) equation. The velocity autocorrelation function obtained is also identical to that given by these authors.