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534. QCFF/PI: Quantum Mechanical Extension of the
Consistent Force-Field Method (VAX Version)
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
Converted by David E. Bugay and Willem R. Leenstra,
Department of Chemistry, University of Vermont,
Burlington, Vermont 05405
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 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.
FORTRAN 77 (VAX)
Lines of Code: 5689
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