  A soft ellipsoid model for Gaussian polymer chains is studied, following an
idea proposed by Murat and Kremer [J. Chem. Phys. 108, 4340 (1998)]. In this
model chain molecules are mapped onto ellipsoids with certain shapes, and to
each shape a monomer density is assigned. In the first part of the work, the
probabilities for the shapes and the associated monomer densities are studied
in detail for Gaussian chains. Both quantities are expressed in terms of simple
approximate formulae. The free energy of a system composed of many ellipsoids
is given by an intramolecular part accounting for the internal degrees of
freedom and an intermolecular part following from pair interactions between the
monomer densities. Structural and kinetic properties of both homogeneous
systems and binary mixtures are subsequently studied by Monte-Carlo
simulations. It is shown that the model provides a powerful phenomenological
approach for investigating polymeric systems on semi-macroscopic time and
length scales.
