Microcanonical ensembles of systems with mechanical constraints (1305.1031v1)

Abstract: We have obtained an exact expression for the phase-space volume corresponding to a microcanonical ensemble of systems under center of mass, total linear and angular momenta conservation constraints, and arbitrary constraints on the coordinates of particles of the system. Methods are suggested to calculate the phase-space volume and density of states from the mean kinetic energy and mean inverse kinetic energy. Methods to control equilibrium in simulations are also presented. We have derived exact formulae for several thermodynamic response functions. It is shown how to obtain the phase-space volume corresponding to other ensembles when one or several of the constraints are removed. It is shown that the phase-space volume of a system at positive values of the energy is a polynomial function of the energy if the potential energy of interaction between particles of the system consists of a hard-core potential and an arbitrary negative potential. We have also shown that the coefficients of the polynomial function can be determined from simulations.