THIS INFORMATION IS OBSOLETE AND IS PROVIDED ONLY FOR ITS HISTORICAL VALUE

by A. Warshel, Department of Chemistry, University of Southern California, Los Angeles, California 90007 and M. Levitt, Department of Chemical Physics, The Weizmann Institute of Science, Rehovot, Israel

The QCFF/PI program is a quantum mechanical extension of the Consistent Force Field Method which allows the application of the CFF method to nonlocalized p- electron systems, i.e., conjugated molecules. The program provides equilibrium geometries (in the Cartesian space), the complete set of normal modes and vibrational frequencies, as well as the p-electron levels (for conjugated molecules). In addition, it is possible to calculate the equilibrium geometries and vibrational frequencies of excited electronic surfaces of conjugated molecules which in turn can be used for calculating the vibrational fine structure of electronic transitions.

The program provides potential surfaces in terms of the 3n Cartesian coordinates of the given molecules. The surface is composed of a set of empirical functions (for the sigma framework) as semi-empirical p integrals which are scaled by the quantum mechanical bond orders. The CFF parameters of the potential functions and the p integrals for hydrocarbons are included in the program. For other molecules, an approximated set of parameters can be used. The potential surface and its first and second derivatives with respect to the Cartesian coordinates are given in an analytical form. These analytical first and second derivatives allow for efficient minimization of the molecular energy by the modified Newton-Raphson method and for straightforward evaluation of the vibrational frequencies by diagonalization of the matrix of mass-scaled second derivatives.

FORTRAN IV (IBM) Lines of Code: 5846