Density profiles of atoms in nano-tubes from an analytic method: hydrogen in a cylindrical pore

Abstract

Knowledge of the structure of simple fluids in nano-tubes constitutes important information in many scientific and technical branches. Computer simulations and density functional theory (DFT) offer accurate but laborious results. We have proposed a simple analytical method to determine the background correlation function on the basis of the residual chemical potentials of a pair of interacting bodies and of the corresponding combined body. These potentials are obtained in terms of geometric quantities. In this paper we dealt with the combination rule for the geometric quantity Q; the harmonic mean rule was proposed and verified at low densities by calculating the third cross-virial coefficient, and by comparing calculated density profiles of the inhomogeneous systems of hard sphere–wall at higher densities. A slight improvement over the previous results were found. Next, we applied our analytic method to realistic systems of a simple molecule in the graphite cylindrical pore. Hydrogen (and carbon monoxide), interacting with carbon of the graphite via the modified LJ potential are considered and the density profile was determined taking into account only the soft-sphere interaction within Weeks–Chandler–Andersen approximation. The considered approach was found to yield a fair description of the realistic simple fluid–cylindrical pore system.