On the thermodynamic perturbation theory for dipolar hard spheres

An equation for the Helmholtz free energy of dipolar media based on thermod ynamic perturbation theory was obtained. As distinguished from the traditio nally selected base system of hard spheres, the base system of thermodynami c perturbation theory used in this work was that of particles interacting w ith a centrally symmetrical potential. The suggested model included a varia tional parameter with dimension of energy selected in such a way as to take into account orientation interaction effects (this somewhat simplified the perturbation theory expansion for the Helmholtz free energy and substantia lly simplified the expression for the distribution function of a dipolar sy stem in comparison with perturbation theory expansion with the use of the b ase function of hard spheres). The suggested approach was shown to be capab le of providing similar expansions taking into account quadrupole interacti ons in polar systems.