The Approach to Equilibrium and Molecular Dynamics

Abstract

Some of the first studies in Molecular Dynamics were already concerned with the problem of approach to equilibrium. Alder and Wainwright¹ and later Bellemans and Orban² have calculated the time evolution of the Boltzmann H-function for a dilute gas of hard disks and hard spheres put initially in a non-equilibrium state. This was realized by choosing initial velocities of particles having all the same magnitude but pointing in random directions. These simulations have shown that the irreversible behavior predicted by Boltzmann already appears for systems made of a few hundred particles; these experiments have also illustrated the fact that MD trajectories in phase space are accurate over a few collision times only, as can be seen by reversing the particle velocities.