Hi All - I am reading a paper "Comparison of AMBER, CHARMM, COMPASS, GROMOS, OPLS, TraPPE, and UFF forcefield for prediction of vapor-liquid coexistence curves and liquid densities." By M.G. Martin, 2006, in Fluid Phase Equilibria.
He discusses "Geometric mean mixing rules" versus "Lorentz-Berthelot" mixing rules.
For the latter is shown,
e(ij)=k(ij)*sqrt(e(ii)*e(jj)), where k(ij) is an empirical constant and
a(ij)=l(ij)*sqrt(a(ii)*a(jj)), where l(ij) is an empirical constant.
Does this mean that Lorentz-Berthelot mixing rules require every pair of atoms' van der waals interactions to be empirically fit to experiment? I thought the entire point of "mixing rules" was to take an atom pair parameter, e.g. e(ij) and make it dependent on two single atom parameters, e.g. e(ii) and e(jj).
Daniel J. Sandberg
University of Connecticut
Department of Chemistry
Birge Research Group