  Coulomb interactions are present in a wide variety of all-atom force fields.
Spherical truncations of these interactions permit fast simulations but are
problematic due to their incorrect thermodynamics. Herein we demonstrate that
simple analytical corrections for the thermodynamics of uniform truncated
systems are possible. In particular results for the SPC/E water model treated
with spherically-truncated Coulomb interactions suggested by local molecular
field theory [Proc. Nat. Acad. Sci. USA 105, 19136 (2008)] are presented. We
extend results developed by Chandler [J. Chem. Phys. 65, 2925 (1976)] so that
we may treat the thermodynamics of mixtures of flexible charged and uncharged
molecules simulated with spherical truncations. We show that the energy and
pressure of spherically-truncated bulk SPC/E water are easily corrected using
exact second-moment-like conditions on long-ranged structure. Furthermore,
applying the pressure correction as an external pressure removes the density
errors observed by other research groups in NPT simulations of
spherically-truncated bulk species.
