Monte Carlo and integral-equation studies of hard-oblate-spherocylinder fluids.

Abstract

Hard-oblate spherocylinders with reduced core diameters ${\mathit{l}}^{\mathrm{*}}$=l/\ensuremath{\sigma}=1, 2, 3 are studied at several packing fractions up to \ensuremath{\eta}=0.45. Monte Carlo results are given for the first six spherical harmonic coefficients of the pair distribution function, ${\mathit{g}}_{\mathit{k}\mathit{l}\mathit{m}}$(r), and for the compressibility factors. These results are compared with the hypernetted chain (HNC), Percus-Yevick (PY), and modified Verlet (VM) approximations. The VM theory produces very good results for the ${\mathit{g}}_{000}$ harmonic coefficient at low and medium densities and for the reduced coefficients ${\mathit{g}}_{\mathit{k}\mathit{l}\mathit{m}}^{\mathrm{*}}$=${\mathit{g}}_{\mathit{k}\mathit{l}\mathit{m}}$/${\mathit{g}}_{000}$ at all densities considered. The PY and HNC results are less accurate and none of the theories satisfactorily describes the ${\mathit{g}}_{000}$ harmonic coefficient at \ensuremath{\eta}=0.45. The VM theory gives equation-of-state results in excellent agreement with the simulation data, whereas the PY values of the compressibility factors at medium and high densities are too low while the HNC values are too high. The thermodynamic consistency between the pressure and the compressibility equations is also tested for each of the PY, HNC, and VM theories. At all state points considered the consistency of the VM theory is much better than that of the PY and HNC theories. Finally, we report results for the first bridge diagram (the first term in the density expansion of the bridge function) at several specific orientations of the root molecules.