Quantifying the effects of neglecting many-body interactions in coarse-grained models of complex fluids

We describe a general simulation scheme for assessing the thermodynamic consequences of neglecting manybody effects in coarse-grained models of complex fluids. The method exploits the fact that the asymptote
of a simple-to-measure structural function provides direct estimates of virial coefficients. Comparing the virial
coefficients of an atomistically detailed system with those of a coarse-grained version described by pair potentials,
permits the role of many-body effects to be quantified. The approach is applied to two models: (i) a sizeasymmetrical colloid-polymer mixture, and (ii) a solution of star polymers. In the latter case, coarse-graining to
an effective fluid described by pair potentials is found to neglect important aspects of the true behavior.