|
QCMP128. ASYM20: A Program for Force Constant and Normal
Coordinate Analysis
by Lise Hedberg, Department of Chemistry, Oregon State
University, Corvallis, Oregon 97331 and Ian M. Mills,
Department of Chemistry, University of Reading, Reading
RG6 2AD, England
Program ASYM20 is a normal coordinate program which may
be used to refine force constants in the harmonic
approximation using the following experimental data:
wave numbers, isotopic wavenumber shifts, Coriolis
coupling constants, root-mean-square amplitudes of
vibration, and centrifugal distortion constants. The
name ASYM20 is intended to indicate that the
calculations may be carried out for molecules of any
symmetry with up to 20 atoms. The program has special
provisions for handling molecules of higher symmetry,
specifically molecules with doubly and triply
degenerate normal modes.
The theory behind the calculations, and the way it is
implemented in the program, is discussed in the paper
by Lise Hedberg and Ian Mills, "ASYM20: A Program for
Force Constant and Normal Coordinate Calculations, with
a Critical Review of the Theory Involved", which is
scheduled for publication in the Journal of Molecular
Spectroscopy in the spring of 1993.
The refinement is usually carried out using symmetrized
force constants. For small molecules where there are
no redundancies, it is possible to carry out a
refinement based on valence force constants. If
redundancies are present, these must be eliminated
before the calculations can be carried out.
The structure of the molecule is entered in the form of
Cartesian coordinates, and the symmetry coordinates are
defined by use of the U-matrix. When symmetry
coordinates are used, the G-matrix will be blocked
according to symmetry species, and the program will
calculate normal coordinates for one symmetry species
at a time. These will be kept separate throughout the
calculations. Consequently, the observed wavenumbers
must be entered according to the symmetry species to
which they belong.
There is no provision in the program for calculation of
Urey-Bradley coordinates, but if these are known, they
may be entered in terms of the Z-matrix, and the
refinement may be carried out based on Urey-Bradley
force constants.
The FORTRAN code has been written in very simple form
to make it easy to transfer the program to different
computers. But there are two statements, CALL DATE and
CALL TIME, which are dependent on the compiler and the
operating system one is using. The information
obtained from these calls is listed at the top of the
output file, and we find it useful. It may be
necessary to write a small subroutine to make these
calls compatible with the computer one is using.
Lines of Code: 5647
FORTRAN (Microsoft 5.0)
|
