  Given the ubiquity of depletion effects in biological and other soft matter
systems, it is desirable to have coarse-grained Molecular Dynamics simulation
approaches appropriate for the study of complex systems. This paper examines
the use of two common truncated Lennard-Jones (WCA) potentials to describe a
pair of colloidal particles in a thermal bath of depletants. The shifted-WCA
model is the steeper of the two repulsive potentials considered, while the
combinatorial-WCA model is the softer. It is found that the depletion-induced
well depth for the combinatorial-WCA model is significantly deeper than the
shifted-WCA model because the resulting overlap of the colloids yields extra
accessible volume for depletants. For both shifted- and combinatorial-WCA
simulations, the second virial coefficients and pair potentials between
colloids are demonstrated to be well approximated by the Morphometric
Thermodynamics (MT) model. This agreement suggests that the presence of
depletants can be accurately modelled in MD simulations by implicitly including
them through simple, analytical MT forms for depletion-induced interactions.
Although both WCA potentials are found to be effective generic coarse-grained
simulation approaches for studying depletion effects in complicated soft matter
systems, combinatorial-WCA is the more efficient approach as depletion effects
are enhanced at lower depletant densities. The findings indicate that for soft
matter systems that are better modelled by potentials with some
compressibility, predictions from hard-sphere systems could greatly
underestimate the magnitude of depletion effects at a given depletant density.
