A method for the simulation of fluids confined between surfaces is developed. The molecular dynamics, with coupling to an external bath, simulation method of Berendsen et al. [J. Chem. Phys. 81, 3684 (1984)] is extended for this purpose. We keep the temperature and the parallel component of pressure fixed and change the box length in the perpendicular direction with respect to the confining surfaces to archive equilibrium. The simulation is easy to perform, especially in the case of solvation force computation. Employing this method, the simulation results on the confined Lennard-Jones and water are presented and are compared to previous grand canonical ensemble Monte Carlo and molecular dynamics simulation results. While consistent with other methods, our results show that spherical Lennard-Jones particles and water form layered structures parallel to the confining surfaces with enhanced layering with increasing pressure. Also we studied the oscillatory behaviors of solvation force and number density of confined particles as well as the stepwise variation of particle numbers as a function of separation between confining surfaces.

A method for performing molecular dynamics simulation in the grand canonical ensemble is developed. The molecular dynamics, with coupling to an external bath, simulation method of [Berendsen et al., J. Chem. Phys. 81, 3684 (1984)] is extended for this purpose. Here the physical system of interest consists of real indistinguishable particles plus one fractional particle, whose potential energy of interaction with the rest of particles is scaled by a coupling parameter, ranging dynamically between zero and one. This coupling changes the number of particles in the system gradually and dynamically, depending on the target values of the excess chemical potential, temperature, and volume. A nonlinear scaling scheme has been adopted to scale the potential energy of interaction of the fractional particle with the rest of the system. The method has been employed to predict the density of compressed Lennard-Jones fluid, compatible with the target values of temperature and the excess chemical potential, over a wide range of temperatures and densities. The method has further been applied to do molecular dynamics simulation in the grand canonical ensemble for water and to predict its vapor-liquid phase coexistence point. The results obtained using this method are in complete agreement with previously reported results in the literature.

Local order parameters for the characterization of liquid and different two- and three-dimensional crystalline structures are presented. The order parameters are expressed in terms of the angular correlations between a vector (defined in terms of the spherical harmonics, identifying the local environment around a central particle) and its neighboring vectors. For the three-dimensional systems, we have undertaken simulation of the Lennard-Jones (12-6) particles and metallic systems at the melting temperature. The proposed order parameters are shown to accurately discriminate between liquid, fcc, hcp, and bcc phases. The simulated two-dimensional systems consist of liquid, Kagome, square, honeycomb, and hexagonal phases formed from a solution of triblock Janus colloidal particles, sedimented on the top of a supporting surface. The presented order parameters resolve all phases. A comparison was made between the predictive ability of the present order parameters and the popular three-dimensional [Lechner and Dellago, J. Chem. Phys., 2008, 129, 114707] and two-dimensional [Mermin, Phys. Rev., 1968, 176, 250] order parameters in the literature in the identification of crystal structures. In both cases, advancements in the present scheme, over the existing methods in the literature, are seen.