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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) |