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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.

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.