EFFICIENT TREATMENT OF OUT-OF-PLANE BEND AND IMPROPER TORSION INTERACTIONS IN MM2, MM3, AND MM4 MOLECULAR MECHANICS CALCULATIONS

Simple and very efficient formulas are presented for four-body out-of- plane bend (used in MM2 and MM3 force fields) and improper torsion (us ed in the MM4 force field) internal coordinates and their first and se cond derivatives. The use of a small set of bend and stretch. intermed iates allows for order of magnitude decreases in calculation time for potential energies and their first and second derivatives, which are r equired in molecular mechanics calculations. The formulas are eminentl y suitable for use in molecular simulations of systems with complicate d bond networks. (C) 1997 John Wiley & Sons, Inc.