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Manuscript Title: TRIATOM: for the calculaton of ro-vibrational spectra of triatomic molecules.
Authors: J. Tennyson, S. Miller, C.R. Le Sueur
Program title: TRIATOM
Catalogue identifier: ABJW_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 75(1993)339
Programming language: Fortran.
Computer: Convex C3840.
Operating system: BSD UNIX.
Word size: 32
Peripherals: disc.
Keywords: Molecular physics, Vibration, Ro-vibrational, Body-fixed, Finite basis Representation, Gaussian quadrature, Variational, Vectorised.
Classification: 16.3.

Subprograms used:
Cat Id Title Reference
ABJX_v2_0 SELECT CPC 75(1993)339

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 [1].

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 [2]. TRIATOM provides data necessary to drive ROTLEVD [3] and DIPOLE [4].

Restrictions:
The size of matrix that can practically be diagonalised. TRIATOM dimensions 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:
Highly case dependent. The sample data takes 17 sec for J=0 and 30 sec for J=1 (Coriolis decoupled) on the Convex C3840.

References:
[1] B.T. Sutcliffe and J. Tennyson, Intern. J. Quantum Chem. 29(1991)183
[2] J. Tennyson, S. Miller, C.R. Le Sueur, this article, second program (SELECT).
[3] J. Tennyson, S. Miller, C.R. Le Sueur, this article, third program (ROTLEVD)
[4] J. Tennyson, S. Miller, C.R. Le Sueur, this article, fourth program (DIPOLE).