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Manuscript Title: MOLFORCE: a computer program for calculation of molecular force constants using the generalized inverse matrix.
Authors: B. Gellai
Program title: MOLFORCE
Catalogue identifier: AABG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 36(1985)177
Programming language: Fortran.
Computer: ES-1040.
Operating system: OS 21.8F.
RAM: 72K words
Word size: 8
Keywords: Molecular force Constants, Vibration, Generalized matrix Inverse, Weighted least squares Method.
Classification: 16.3.

Revision history:
Type Tit le Reference
correction 000A CORRECTION 29/01/86 See below

Nature of problem:
The program calculates the molecular force constants, i.e. the elements of the potential energy matrix F and their dispersions, by fitting the isotope substituted frequency data by means of the weighted least squares method. The convergence difficulties of the iteration process that may be caused by an ill conditioned Jacobian matrix are eliminated. Determinacy of the obtained molecular force field can be decided at the end of iteration.

Solution method:
Elimination of the convergence difficulties of the least squares method is achieved by application of the generalized matrix inverse of the Jacobian. The method takes the rank of a (nearly) singular Jacobian into account and substitutes it by one of a lower rank which is near to it and well conditioned thereby transforming the given physical problem into the space spanned by the independent column vectors of the Jacobian. The structure of the projector matrix J+J where J+ is the generalized inverse of the Jacobian gives information about the statistical determinacy of the obtained force constants.

Restrictions:
If there is internal coordinate redundance it should be removed before using the program.

Running time:
It depends on the problem - about 3-5 s for the test runs.

CORRECTION SUMMARY
Manuscript Title: MOLFORCE: a computer program for calculation of molecular force constants using the generalized inverse matrix. (C.P.C. 36(1985)177).
Authors: B. Gellai
Program title: 000A CORRECTION 29/01/86
Catalogue identifier: AABG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 39(1986)447
Classification: 16.3.