CAN THE LENNARD-JONES 6-12 FUNCTION REPLACE THE 10-12 FORM IN MOLECULAR MECHANICS CALCULATIONS

A protocol to replace "10-12" hydrogen bonding function with the "6-12" form to reproduce hydrogen bond distances, energies, and geometries in molecular mechanics calculations is described. The 6-12 function was least-squares fit to the normally employed 10-12 form of the function for the hydrogen bond types of the Weiner et al. force field by iterating over the A and B coefficients. A weighting function was used to fit the curves in the most critical areas. The 6-12 hydrogen bond model was compared with the Weiner et al. force field, OPLS/AMBER fore field, and quantum mechanical calculations on two simple systems, the water dimer and the chloride-water interaction. The 6-12 model produced structures, energies, and geometries that were consistent with the other molecular mechanics calculations and showed reasonable agreement to the quantum mechanical results for the water dimer. The 6-12 model was also compared with normal calculations using a 10-12 model on several representative systems. The results indicate that the 6-12 function, when substituted by the procedure outlined in this work, yields structures and hydrogen bond properties that are similar to the normal 10-12 model.