Finite-size effects in molecular dynamics simulations: Intermediate scattering function and velocity of sound. III. Theory and application to a modelkrypton fluid - art. no. 051201

We describe a method for obtaining the intermediate scattering function I(Q ,t) from a computer simulation: it is an extension of our earlier calculati on [Salacuse, Denton, and Egelstaff, Phys. Rev. E 53, 2382 (1996)] for the t-->0 limit. We use this approach to obtain I(Q,t) for low Q and t from mol ecular dynamics (MD) simulations of a model krypton fluid whose atoms inter act via a truncated Aziz pair potential, and the results are compared over their range of validity to I(Q,t) determined by the standard MD method and also by a time expansion approach. In its range of validity our approach is much more efficient than the standard MD method; however, it covers a rest ricted range of t due to the movement of density fluctuations (sound waves) through the simulated fluid which produces an anomaly in the time behavior of I(Q,t). By analyzing I(Q=0,t) the velocity of sound in the simulation i s determined, and the results compare favorably with published experimental results for the sound velocity of liquid krypton.