A COMPARISON BETWEEN COLLISIONAL DYNAMICS AND BROWNIAN DYNAMICS

This paper presents an analytical investigation for the velocity relaxation of a test particle coupled to a heat bath by two different mechanisms: the Brownian dynamics (ED) and the collisional dynamics (CD). Relation between the parameters of the methods is established. The velocity relaxation spectrum induced by the coupling in the CD method is shown to be different from the one in the ED method. The difference between the spectra disappears in the limit gamma --> O, where gamma is a mass ratio of the bath atoms and the test particle.