Lengthy (120ns) simulations of guest molecules confined in zeolite NaCaA, as well as that of pure fluid, were carried out on the microcanonical ensemble in order to obtain an estimate of the error associated with the diffusion coefficient. It was found that the error was about 50% for a 1ns run for argon parameters in NaCaA zeolite. Shorter runs led to an overestimation of the value of the diffusion coefficient. It was also found that a linear fit to a region of the mean square displacement below ∼200ps led to an overestimation of the diffusion coefficient. For runs that were sufficiently long, the initial configuration had no effect upon the diffusion coefficient. The values obtained from the mean square displacement and the velocity autocorrelation function converged for the runs reported. It was shown that the error in the diffusion coefficient depended upon the nature of the system and its underlying potential energy surface. The calculated statistical inefficiency suggested that averages of properties such as the total energy would be uncorrelated over blocks longer than 150ps. A dependence of the error in diffusion coefficient upon the simulation length and size was reported.

Estimation of Error in the Diffusion Coefficient from Molecular Dynamics Simulations. R.Chitra, S.Yashonath: Journal of Physical Chemistry B, 1997, 101[27], 5437-45