CALCULATION OF INTRAMOLECULAR FORCE-FIELDS FROM 2ND-DERIVATIVE TENSORS

A practical procedure (FUERZA) to obtain internal force constants from Cartesian second derivatives (Hessians) is presented and discussed. I t allows a systematic analysis of pair atomic interactions in a molecu lar system, and it is fully invariant to the choice of internal coordi nates of the molecule. Force constants for bonds or for any pair of at oms in general are defined by means of the eigenanalysis of their pair interaction matrix. Force constants for the angles are obtained from their corresponding two-pair interaction matrices of the two bonds or distances forming the angle, and the dihedral force constants are simi larly obtained using their corresponding three-pair interaction matric es. (C) 1996 John Wiley & Sons, Inc.