AMBER-ii: New Combining Rules and Force Field for Perfluoroalkanes

A molecular mechanics force field
of the AMBER/OPLS family for
perfluoroalkanes, noble gases, and their mixtures with alkanes has
been proposed. We had to abandon the traditional Lorentz–Berthelot
combining rules for the Lennard-Jones potential to be able to uniformly
describe these substance classes and their mixtures. Instead, the
Waldman-Hagler rules developed for noble gases were used for all of
these elements except hydrogen. Hydrogen is considered to be a particular
substance to which the usual Lorentz–Berthelot rules are applied.
The proposed rules have little effect on the organic chemistry of
H, C, N, and O elements but make it compliant with the chemistry of
heavy elements. Because of assigning a relatively high partial charge
of −0.37e to fluorine atoms, the new force
field reproduces the mutual insolubility of higher liquid alkanes
and perfluoroalkanes.