ATOMIC TRANSPORT IN A RANDOM ALLOY FROM THE MOMENTS OF TIME-CORRELATION FUNCTIONS

The phenomenological coefficients for matter transport in a random bin ary alloy can all be calculated from the time integral of a single tim e correlation function C(t). Exact expressions for the coefficients (m oments) in the Taylor expansion of C(t) in powers of t have been calcu lated for terms up to t(4). The moments have been used to construct ap proximations for C(t) and for the phenomenological coefficients by mea ns of the Mori continued-fraction representation of the Laplace transf orm, by a method based on a result in the Kirkwood transport theory of liquids, and by means of Pade approximants. The results have been com pared with earlier Monte Carlo simulation values. For the first two me thods the predictions of phenomenological coefficients are better than those of the path probability expressions of Sate and coworkers but d o not approach the remarkable accuracy of the Manning theory. The inad equacies of our results arise because the approximate time correlation functions are smaller than the Monte Carlo results at long times.