In inhomogeneous systems the diffusion paths available to particles are often restricted by the topology of the system itself. In search of a realistic scheme to simulate such inhomogeneous systems, we developed a new method, of local control of the chemical potential. The local control method, which limits creation and destruction of particles to a control volume, can be successfully implemented in both Monte Carlo (MC) and molecular dynamics (MD) simulations of the grand canonical ensemble (GC). We present applications of local GCMC calculations of the one-dimensional lattice gas and hard rods confined by hard walls, as well as local GCMC and GCMD of a three-dimensional bulk Lennard-Jones fluid system. The simulation results compare successfully with analytical solutions and equation of state approximations.

We study the dynamic response of confined liquid films to shear with molecular dynamics simulations. Both the hydrostatic pressure and chemical potential are controlled during the shearing process. We introduce grand canonical molecular dynamics to allow for material fluctuations.

We present results for the vapour-liquid coexistence properties of dipolar diatomic fluids modelled using interaction site potentials, calculated via a recently developed theory which is based upon resummations of interaction site cluster expansions. The model under consideration is a homonuclear diatomic with site-site Lennard-Jones interactions and dipole-dipole interactions produced by the presence of a discrete charge distribution obtained by placing a positive charge on one site and a negative charge upon the other. The theory includes contributions to the free energy beyond first order through resummation of the interaction site cluster expansions of the correlation functions and the Helmholtz free energy. The theoretical results are used to describe the effects of molecular shape and polarity upon the phase diagram.

We present results for the structure and thermodynamics of the dipolar hard dumbbell fluid obtained from a recently developed theory which is based on an extension of cluster perturbation theory (CPT) for atomic fluids to the interaction site formalism. The calculations are for the lowest order result in the theory which we denote as the optimized random phase approximation in the interaction site formalism (ISF-ORPA). This method does not include unallowed diagrammatic contributions to the structure and thermodynamics, in contrast to previous CPTs in the interaction site formalism. We compare the results to computer simulation data and find that the theory gives a realistic representation of the effect of the electrostatic interactions on the structure of the fluid.

We present a new approach to the theory of clustering and percolation phenomena in assemblies of nonspherical particles. The method is based on an interaction site formalism. By treating each particle in the assembly as a collection of interaction sites we are able to formulate the connectivity problem in terms of a site–site pair connectedness function, Pαβ(r). Through adaptation of existing results in the theory of pair correlations in interaction site systems the cluster expansion of Pαβ(r) has been obtained and two Ornstein–Zernike-like integral equations are developed through which Pαβ(r) may be calculated. As an illustration of the approach results are presented for a system consisting of dumbbells randomly distributed in a matrix.

We describe a method for determining the contributions to the structure and thermodynamics of interaction site fluids arising from long-ranged perturbations to the site–site potential. An extension of cluster perturbation theories developed for atomic fluids (optimized cluster theory, Γ ordering) to the interaction site cluster expansion is the basis of the new theory. Given the pair distribution function and the Helmholtz free energy of the reference system, the theory predicts the contribution to the structure and Helmholtz free energy arising from a perturbation to the potential, and contains no nonphysical contributions such as those arising in previous theories for these systems. Various levels of approximation are possible within the theory. We discuss the lowest level in detail. This is the extension of the optimized random phase approximation to the interaction site formalism (ISF-ORPA). The relationship with integral equation theories for these systems is established.

We present a study of solutions of the site-site Omstein-Zernike equation in the hypernetted chain (HNC) approximation (the extended RISM equation) in the critical region for diatomic fluids modeled with site-site 12-6 potentials and point charge dipoles. The results exhibit anomalies beyond those found in the HNC approximation for atomic fluids. For small bond lengths isotherms of the bulk modulus show considerable asymmetry with respect to the critical density and for some temperatures a local minimum at high density. For systems with large bond lengths the results are similar to those for atomic fluids.