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Manuscript Title: TRIATOM, SELECT and ROTLEV: for the calculation of the ro-vibrational levels of triatomic molecules.
Authors: J. Tennyson
Program title: TRIATOM
Catalogue identifier: AALO_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 42(1986)257
Programming language: Fortran.
Computer: CRAY -1.
Program overlaid: yes
Peripherals: disc.
Keywords: Molecular physics, Vibration, Ro-vibrational, Body-fixed, Associated laguerre Polynomials, Associated legendre Polynomials, Gaussian quadrature, Variational.
Classification: 16.3.

Subprograms used:
Cat Id Title Reference
AALP_v1_0 SELECT CPC 42(1986)257

Nature of problem:
TRIATOM calculates the bound ro-vibrational levels of a triatomic system using the generalised body-fixed coordinates developed by Sutcliffe and Tennyson.

Solution method:
A basis is constructed as a product of radial (either Morse oscillator- like or spherical oscillator) functions and associated Legendre polynomials for the bending coordinate, with rotation matrices carrying the rotational motion. A secular matrix is constructed using Gaussian quadrature and diagonalised to give the solutions. The method is variational allowing basis set parameters to be optimised. Input can either be direct or from SELECT. TRIATOM gives the data necessary to drive ROTLEV.

Restrictions:
The size of matrix that can practically be diagonalised. TRIATOM allocates arrays dynamically at execution time and in the present version the total space available is a single parameter which can be preset as required.

Unusual features:
A user supplied subroutine containing the potential energy as an analytic function (optionally a Legendre polynomial expansion) is a program requirement.

Running time:
Case dependent but domainated by matrix diagonalisation. A problem with 533 basis functions (requiring 350000 words storage) takes 8 seconds on the CRAY-1.