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Manuscript Title: A program suite for the calculation of ro-vibrational spectra of triatomic molecules.
Authors: J. Tennyson, S. Miller
Program title: TRIATOM
Catalogue identifier: ABJW_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 55(1989)149
Programming language: Fortran.
Computer: CRAY-1.
Operating system: COS.
Peripherals: disc.
Keywords: Molecular physics, Vibration, Ro-vibrational, Body-fixed, Associated laguerre Polynomials, Associated legendre Polynomials, Gaussian quadrature, Variational, Close-coupled equations, Vectorised.
Classification: 16.3.

Subprograms used:
Cat Id Title Reference
ABJX_v1_0 SELECT CPC 55(1989)149

Nature of problem:
TRIATOM calculates the bound ro-vibrational levels of a triatomic system using the generalized 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 solutions. Input can be direct from SELECT. TRIATOM provides data necessary to drive ROTLEVD and DIPOLE.

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 reset 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 dominated by matrix diagonalisation. A problem with 600 basis functions (requiring 350000 words storage) takes 9 seconds on the CRAY XMP-48.