ON ALGORITHMS FOR BROWNIAN DYNAMICS COMPUTER SIMULATIONS

Several Brownian Dynamics numerical schemes for treating stochastic differential equations atthe position Langevin level are analyzed from the point of view of their algorithmic efficiency. The algorithmsare tested using model colloidal fluid of particles interacting via the Yukawa potential. Limitationsin the conventional Brownian Dynamics algorithm are shown and it is demonstrated that much betteraccuracy for dynamical and static quantities can be achieved with an algorithm based on the stochasticexpansion and second-order stochastic Runge-Kutta algorithms. Mutual merits of the second-order algorithmsare discussed.Pozna

Orientational correlations in s u s p e n s i o nof r o d l i k e colloidal macroparticles

Orientational correlations of rodlike colloidal particles interactingvia a two-site Yukawa potential are investigated using Brownian dynamics computersimulations. It is found that the orientational relaxation proceeds in threedifferent regimes: very short-time regime, diffusive and long-time nondiffusive.An influence of particle concentration, the one-particle diffusion tensor, and particleelongation on these regimes is discussed.Pozna

Nonperiodic solid phase in a two-dimensional hard-dimer system

We report Monte Carlo simulations of a system of two-dimensional, hard, homonuclear dimers. The equation of state and the Gibbs free energy were computed for the fluid phase and several crystalline and noncrystalline (aperiodic) solid structures. We observe that the differences in Gibbs free energy between the various solid structures are much less than the contribution to the entropy due to degeneracy of the ‘‘ground state’’ of the aperiodic solid. Hence, the thermodynamically stable solid structure of the system corresponds to an aperiodic arrangement of the molecular centers of mass and orientations. The melting point determined for this aperiodic solid is located within the observed narrow hystersis region