BACKWARD EULER AND OTHER METHODS FOR SIMULATING MOLECULAR FLUIDS

Two implementations of the backward Euler method for simulating molecu lar fluids are compared : with Brownian dynamics and molecular dynamic s simulations of a single diatomic molecule, liquid argon, a single bu tane molecule, and liquid butane. By comparison with standard molecula r dynamics results, backward Euler simulations give different thermody namic properties for liquids; predict liquid structures which are too solidlike; and incorrectly represent dynamical relaxation processes. T he backward Euler methods allows longer time steps to be used in simul ations at-the cost of an energy minimization at every time step. Even when time steps more than 20 times larger than that required for energ y and momentum conservation are used, neither implementation of the ba ckward Euler algorithm is more accurate than standard molecular dynami cs calculations with the same time step. We conclude that the new meth ods offer no computational advantages over more usual methods for simu lating molecular fluids and that they often predict incorrect results. (C) 1995 American Institute of Physics.