The time-correlation functions which were associated with the Onsager phenomenological coefficients for isothermal matter transport were calculated, for a binary system, by using Monte Carlo techniques. This was done for the equi-atomic composition according to the Kikuchi-Sato model for an order-disorder alloy with a vacancy transport mechanism. The diagonal time-correlation functions were positive, decayed monotonically to zero, and exhibited a long-term tail where they varied as t-n; with n varying slightly with temperature at high temperatures, and more rapidly as the temperature was lowered through the order-disorder transition temperature. In the region of short-range order, the off-diagonal time-correlation function was negative but otherwise exhibited a similar behavior to that of the diagonal function; although, as the transition temperature was approached, n varied more rapidly. At the transition temperature and below, the off-diagonal time-correlation function increased from an initially negative value to a positive maximum, and later in time decreased to zero.

Computer Simulation of Time Correlation Functions and Matter Transport Coefficients for a Model Order-Disorder Alloy. Z.Qin, A.R.Allnatt, E.L.Allnatt: Canadian Journal of Chemistry, 1998, 76[11], 1548-53