ON THE CALCULATION OF THE SINGLE-PARTICLE MOMENTUM AND ENERGY-DISTRIBUTIONS FOR A HARD-CORE FLUID IN THE MICROCANONICAL MOLECULAR-DYNAMICS ENSEMBLE

The microcanonical molecular dynamics ensemble describes a system with a fixed number of particles in a given volume and with constant total energy and total linear momentum. The primary phase integrals of this ensemble for a hard-core fluid are derived by using geometrical argum ents. The single-particle momentum distribution function is derived by means of a Khinchin decomposition in the momentum-space of the system under study. The momentum moduli distribution and the energy distribu tion are also derived. These distributions are compared with the corre sponding to the microcanonical and canonical ensembles. We show that f or systems with few particles, the differences are significant. This f act could be important in the analysis of the results obtained from mo lecular dynamics of systems with periodic boundary conditions and a sm all number of particles.