  In an effort to generalize the self-consistent Ornstein-Zernike approximation
(SCOZA) -- an accurate liquid-state theory that has been restricted so far to
hard-core systems -- to arbitrary soft-core systems we study a combination of
SCOZA with a recently developed perturbation theory. The latter was constructed
by Ben-Amotz and Stell [J. Phys. Chem. B 108,6877-6882 (2004)] as a
reformulation of the Week-Chandler-Andersen perturbation theory directly in
terms of an arbitrary hard-sphere reference system. We investigate the accuracy
of the combined approach for the Lennard-Jones fluid by comparison with
simulation data and pure perturbation theory predictions and determine the
dependence of the thermodynamic properties and the phase behavior on the choice
of the effective hard-core diameter of the reference system.
