Local chemical potential and pressure tensor in inhomogeneous nanoconfined fluids

There are many simulations in the literature to study the behavior of nanoconfined fluids between solid surfaces. Among them, a class of methods focuses on tuning the pore width in such a way that the fluid in confinement has the same tangential component of pressure as the bulk fluid. The main idea behind these methods is based on the ansatz that in equilibrium (between the fluid in confinement and the bulk fluid) the tangential component of pressure of the confined fluid is equal to the pressure of the bulk fluid at the same temperature. As there is no evidence in the literature on the validity of this ansatz, in this work we have performed molecular dynamics simulations on a large number of nanoconfined Lennard-Jones systems to evaluate its validity. For this purpose, big simulation boxes are chosen, to enable us to directly calculate the particle-particle interactions, and hence, reduce the long-range corrections to the local pressures and local chemical potentials in the inhomogeneous fluid. Simulating the confined fluid at an average tangential component of pressure equal to the pressure of the bulk fluid at the same temperature, we have calculated the chemical potentials in the pore and compared them with the corresponding bulk value. Our calculated results indicate that the chemical potentials in the pore show oscillatory behavior with respect to the pore width. Pronounced deviations in the chemical potentials from the corresponding bulk value are observed in narrower pores, compared to wider pores. Therefore, the results of the present simulations rule out the validity of the above-mentioned ansatz.