  Two liquid state theories, the self-consistent Ornstein-Zernike equation
(SCOZA) and the hierarchical reference theory (HRT) are shown, by comparison
with Monte Carlo simulations, to perform extremely well in predicting the
liquid-vapour coexistence of the hard core Yukawa (HCY) fluid when the
interaction is long range. The long range of the potential is treated in the
simulations using both an Ewald sum and hyperspherical boundary conditions. In
addition, we present an analytical optimised mean field theory which is exact
in the limit of an infinitely long range interaction. The work extends a
previous one by Caccamo et al [Phys. Rev. E,60, 5533 (1999)] for short range
interactions.
