  There exist methods for determining effective conservative interactions in
coarse grained particle based mesoscopic simulations. The resulting models can
be used to capture thermal equilibrium behavior, but in the model system we
study do not correctly represent transport properties. In this article we
suggest the use of force covariance to determine the full functional form of
dissipative and stochastic interactions. We show that a combination of the
radial distribution function and a force covariance function can be used to
determine all interactions in dissipative particle dynamics. Furthermore we use
the method to test if the effective interactions in dissipative particle
dynamics (DPD) can be adjusted to produce a force covariance consistent with a
projection of a microscopic Lennard-Jones simulation. The results indicate that
the DPD ansatz may not be consistent with the underlying microscopic dynamics.
We discuss how this result relates to theoretical studies reported in the
literature.
