We develop a general method to study inhomogeneous liquids in an external field using orthogonal polynomials tailored to the one-body density. The procedure makes integral equation calculations of these systems no more difficult than those of ordinary homogeneous molecular fluids. We apply this method to the ferromagnetic Heisenberg spin fluid in a magnetic field using a “reference” version of the Zerah-Hansen closure, with no further approximations. Comparison with simulation shows this integral equation procedure yielding nearly exact results.

• Received 15 October 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.3535