Numerical test of the nonstationary character of the correlation functions for microcanonical ensembles at short times

Abstract

Abstract Recently Chatzidimitriou-Dreismann has challenged the basic theorem which relates the two stationary correlation functions and of statistical thermodynamics: = - d 2 dt 2 where the dynamical variable B is, for example, a molecular vector. In this paper the theorem is tested to a precision of one part in a million for the unit vectors along the principal molecular moment of inertia axes of an asymmetric top. The rotational velocity correlation function is fitted with a twenty-five term Chebyshev polynomial and the latter is integrated numerically to give a twenty seven term polynomial expression for the orientational a.c.f. The above relation is tested out rigorously for microcanonical ensembles consisting of 108 molecules each of a) compressed hydrogen selenide gas; b) liquid tritium oxide; c) a nonequilibrium but stationary sample of water subjected to an intense uniaxial z axis electric field. Small Dreismann effects are found in cases b) and c) ; effects which are about three orders of magnitude greater than the numerical precision of the fitting method used.