New out-of-plane angle and bond angle internal coordinates and related potential energy functions for molecular mechanics and dynamics simulations

With currently used definitions of out-of-plane angle and bond angle intern al coordinates, Cartesian derivatives have singularities, at +/- pi/2 in th e former case and pi in the latter. If either of these occur during molecul ar mechanics or dynamics simulations, the forces are not well defined. To a void such difficulties, we provide new out-of-plane and bond angle coordina tes and associated potential energy functions that inherently avoid these s ingularities. The application of these coordinates is illustrated by nb ini tio calculations on ammonia, water, and carbon dioxide. (C) 1999 John Wiley & Sons, Inc.