  We implemented a coarse-graining procedure to construct mesoscopic models of
complex molecules. The final aim is to obtain better results on properties
depending on slow modes of the molecules. Therefore the number of particles
considered in molecular dynamics simulations is reduced while conserving as
many properties of the original substance as possible. We address the problem
of finding nonbonded interaction parameters which reproduce structural
properties from experiment or atomistic simulations. The approach consists of
optimizing automatically nonbonded parameters using the simplex algorithm to
fit structural properties like the radial distribution function as target
functions. Moreover, any mix of structural and thermodynamic properties can be
included in the target function. Different spherically symmetric inter-particle
potentials are discussed. Besides demonstrating the method for Lennard--Jones
liquids, it is applied to several more complex molecular liquids such as
diphenyl carbonate, tetrahydrofurane, and monomers of poly(isoprene).
