  We show that spherical truncations of the 1/r interactions in models for
water and acetonitrile yield very accurate results in bulk simulations for all
site-site pair correlation functions as well as dipole-dipole correlation
functions. This good performance in bulk simulations contrasts with the
generally poor results found with the use of such truncations in nonuniform
molecular systems. We argue that Local Molecular Field (LMF) theory provides a
general theoretical framework that gives the necessary corrections to simple
truncations in most nonuniform environments and explains the accuracy of
spherical truncations in uniform environments by showing that these corrections
are very small. LMF theory is derived from the exact Yvon-Born-Green (YBG)
hierarchy by making physically-motivated and well-founded approximations. New
and technically interesting derivations of both the YBG hierarchy and LMF
theory for a variety of site-site molecular models are presented in appendices.
The main paper focuses on understanding the accuracy of these spherical
truncations in uniform systems both phenomenologically and quantitatively using
LMF theory.
