TAYLOR-EXPANSION MONTE-CARLO SIMULATIONS OF CLASSICAL FLUIDS IN THE CANONICAL AND GRAND-CANONICAL ENSEMBLE

In this article the Taylor-expansion method is introduced by which Mon te Carlo (MC) simulations in the canonical ensemble can be speeded up significantly. Substantial gains in computational speed of 20-40% over conventional implementations of the MC technique are obtained over a wide range of densities in homogeneous bulk phases. The basic philosop hy behind the Taylor-expansion method is a division of the neighborhoo d of each atom (or molecule) into three different spatial zones. Inter actions between atoms belonging to each zone are treated at different levels of computational sophistication. For example, only interactions between atoms belonging to the primary zone immediately surrounding a n atom are treated explicitly before and after displacement. The chang e in the configurational energy contribution from secondary-zone inter actions is obtained from the first-order term of a Taylor expansion of the configurational energy in terms of the displacement vector d. Int eractions with atoms in the tertiary zone adjacent to the secondary zo ne are neglected throughout, The Taylor-expansion method is not restri cted to the canonical ensemble but may be employed to enhance computat ional efficiency of MC simulations in other ensembles as well. This is demonstrated for grand canonical ensemble MC simulations of an inhomo geneous fluid which can be performed essentially on a modern personal computer. (C) 1995 Academic Press. Inc.