Percolation Transition in the Parallel Hard-cube Model Fluid

Pressure and self-diffusion calculations for a model fluid system of parallel hard cubes are reported. When viewed alongside equations of state incorporating the known coefficients in the virial expansion (b2 to b7), a weak phase change is postulated around 1/4 close-packing. Changes in behaviour are also seen at the same density for the self-diffusion coefficient and an associated single-particle free volume. It is conjectured that a transition may be identifiable with the low-density percolation transition that occurs in all hard-core fluids when the single particle configurational volume becomes extensive. If the hard-sphere model were to behave similarly, the observations may have implications for the general development of liquid-state theory.