  The structure of a uniform simple liquid is related to that of a reference
fluid with purely repulsive intermolecular forces in a self-consistently
determined external reference field (ERF) phi_ R. The ERF can be separated into
a harshly repulsive part phi_ R0 generated by the repulsive core of a reference
particle fixed at the origin and a more slowly varying part phi_ R1 arising
from a mean field treatment of the attractive forces. We use a generalized
linear response method to calculate the reference fluid structure, first
determining the response to the smoother part phi_ R1 of the ERF alone,
followed by the response to the harshly repulsive part. Both steps can be
carried out very accurately, as confirmed by MD simulations, and good agreement
with the structure of the full LJ fluid is found.
