Integral equation theory for dipolar hard sphere fluids with fluctuating orientational order

We present an integral equation approach to the structural and thermodynamic properties of a fluid of partially aligned dipolar hard spheres. To relate the two-particle correlation functions to the anisotropic singlet density, we mainly employ the Lovett-Mou-Buff-Wertheim equation. We show that, as in the isotropic case, the mean-spherical approximation and the reference hypernetted chain (RHNC) closures lead to quite different results. This is particularly true at high coupling strengths, where the RHNC theory shows a transition from an isotropic to a ferroelectric fluid phase. The predicted transition temperatures are very close to those one obtains from the RHNC theory for the isotropic fluid. (C) 2000 American Institute of Physics. [S0021-9606(00)50707-7].