  The possibility to construct and parametrize the nonbonded interactions in
atomistic force fields based on the valence electron structure of molecules is
explored in this paper. Three different charge distribution models using simple
valence electron based potential functions are introduced and compared. It is
shown that the three models can be constructed such that they only require one
adjustable parameter for the electrostatic potential of a molecule. The
accuracy of the electrostatic potential is evaluated for the three models and
compared to population-derived charges and higher order multipole moments for a
set of 12 small molecules. Furthermore the accuracy and parametrization of the
interaction energies of the three models is evaluated based on ab initio
intermolecular interaction energies. It is shown that the valence electron
potential models provide systematic advantages over conventional point charge
models for the calculation of intermolecular interaction energies even with the
very simple potential functions used here.
