Solid–solid transitions in slit nanopores

The structure of Lennard–Jones (LJ) fluids confined in smooth slit-like pores have been investigated using grand canonical Monte Carlo simulations for a bulk state point lying close to the liquid-solid freezing line. The structure of the fluid is examined by computing the in-plane pair correlation function and bond orientational order parameters. Simulations reveal that the fluid not only freezes into the pore but also undergoes a solid–solid transition from a square to a triangular lattice for small changes in pore widths. This transition occurs at pore widths that accommodate two and three fluid layers. Classification of solid structures based on the 3D counterparts, indicate that the transition occurs between solids that correspond to a body centred tetragonal structure to the hexagonal close packed structure. In the two layer structures the pore fluid consists of the first two basal planes of the bct and hcp structures and in the three layer system a complete unit cell of bct and hcp forms in the direction of confinement.