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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.

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A perturbed hard-sphere equation of state (EOS) has been previously employed to predict pressure-volumetemperature properties of some ionic liquids (ILs) with phosphonium-, pyridinium-, and pyrrolidinium cations. In this work, we have extended the considered EOS to another class of ILs in compressed states. This class consists of 14 imidazolium-based ILs. The predicted densities were compared with those obtained from the experiment, over a broad pressure range from 0.1 to 200 MPa. From 1,122 data points examined for the aforementioned ILs, the total average absolute deviation was found to be 1.05%.

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