Stochastic Liouville equation formalism for translational and rotational diffusiona)

摘要

Stochastic Liouville equations are used to study the relaxation behavior of position and orientation correlation functions of a fluid particle, if the secondhyphen;order velocity or angularhyphen;velocity correlation is given. Two assumptions for reducing higherhyphen;order (angular) velocity correlation functions to twohyphen;point correlation functions are compared, the Gaussian assumption and rsquo;rsquo;the assumption of vanishing higherhyphen;orderGhyphen;cumulants.rsquo;rsquo; In the case of translation both assumptions predict the same diffusion constant; only the latter one yields a Burnett coefficient that diverges in accordance with microscopic results. For rotational diffusion the second assumption is studied and compared with results obtained by Pomeau and Weber on the basis of the first assumption.