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542. QCFF/PI: Quantum Mechanical Extension of the
Consistent Force-Field Method (IBM 3090 Version)
by A. Warshel, Department of Chemistry, University of Southern California, Los Angeles, California 90007 and M. Levitt, Department of Chemical Physics, The Weismann Institute of Science, Rehovot, Israel Converted by F. Sidhu and E. R. Davidson, Department of Chemistry, Indiana University, Bloomington, Indiana 47405 QCPE QCFF/PI program is a quantum mechanical extension of the Consistent Force-Field Method which allows the application of the CFF method to nonlocalized 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 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 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. This version of the program makes use of the IBM Engineering and Scientific Subroutine Library (ESSL) and has been vectorized to some degree. FORTRAN (IBM 3090) Lines of Code: 6000 |