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Manuscript Title: A program for determining primitive semiclassical eigenvalues for vibrating/rotating nonlinear triatomic molecules.
Authors: G.C. Schatz
Program title: ACTION
Catalogue identifier: ABDP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 51(1988)135
Programming language: Fortran.
Computer: HARRIS H1000.
Operating system: VOS.
Word size: 48
Keywords: Semiclassical Eigenvalues, Fourier transform method, Vibrating/rotating Triatomic, Molecules, Vibrations.
Classification: 16.3.

Nature of problem:
This program calculates good actions and primitive semiclassical eigenvalues for vibrating/rotating nonlinear triatomic molecules moving in three dimensions. The program uses the Sorbie-Handy version of the fast Fourier transform method to calculate actions corresponding to the three vibrational normal modes and to a chosen body fixed projection of the rotational angular momentum. Iterative variation of the trajectory initial conditions is used to find the semiclassical root trajectory. Usefulness of this program depends on the simplicity of the power spectra associated with vibrational and rotational motion, and because of this the program requires significant care in making applications. For H2O, once an appropriate set of numerical parameters has been selected, the program uses approximately 5-10 minutes CPU time on a Harris 1000 computer to compute each semiclassical eigenvalue.