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Manuscript Title: III. A force constant adjuster program to obtain a least squares fit to observed frequencies of molecules and crystals.
Authors: F.Y. Hansen
Program title: FYADJ
Catalogue identifier: ACXS_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 14(1978)245
Programming language: Fortran.
Computer: IBM 370/165.
Operating system: OS/MVT RELEASE 21.7.
RAM: 475K words
Word size: 32
Peripherals: disc.
Keywords: Solid state physics, Crystal structure, Neutron, Normal mode, Force constant, Group theory, Vibration molecular, Scattering.
Classification: 7.6, 7.8.

Subprograms used:
Cat Id Title Reference
ACXQ_v1_0 FYCOOR CPC 14(1978)193
ACXR_v1_0 FYFRE CPC 14(1978)219

Revision history:
Type Tit le Reference
correction 000ACORRECTION 28/11/77 See below

Nature of problem:
The objective of the present program is to determine the values of a given set of force constants for the internal vibration of molecules or crystals in the harmonic approximation in such a way as to give a least squares fit of calculated frequencies to observed frequencies.

Solution method:
The calculations with this program are based on the results of FYFRE program described in part II, where data for the generation of the analytic form of the dynamical matrix in terms of relevant force constants have been obtained. The eigenvalues of the Hermitian matrix, which has been blocked diagonalized by symmetry coordinate matrices, are calculated and compared with observed frequencies. An iterative determination of the force constants are performed using a procedure, where only the calculated frequencies need to be entered, while derivatives of the frequencies with respect to force constants do not have to be entered.

The only restriction of the program is the high speed storage available.

Unusual features:
The storage requirement depends on the problem, that is the number of normal modes, and the number of non zero elements of the dynamical matrix. In the present set up the storage requirement is set to 47500 words. Problems with up to 30 normal modes and 500 non zero matrix elements may be considered, while up to 10 force constants may be determined simultaneously in one calculation and up to 100 experimental frequencies may be considered. One should consult the long write up for details.

Running time:
The running time obviously depends in particular on the number of iterations to be performed and to a lesser degree on the nature of the problem. For the test example considered here the running time for 10 iterations were 12 s including compilation time. The compilation time for the program is 7 s.

Manuscript Title: Unpublished correction to III. A force constant adjuster program to obtain a least squares fit to observed frequencies of molecules and crystals.
Authors: F.Y. Hansen
Program title: 000ACORRECTION 28/11/77
Catalogue identifier: ACXS_v1_0
Distribution format: gz
Classification: 7.6, 7.8.