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Manuscript Title: New vibration-rotation code for tetraatomic molecules exhibiting wide-amplitude motion: WAVR4.
Authors: Igor N. Kozin, Mark M. Law, Jonathan Tennyson, Jeremy M. Hutson
Program title: WAVR4
Catalogue identifier: ADUN
Journal reference: Comput. Phys. Commun. 163(2004)117
Programming language: Fortran 90.
Computer: Developed under Tru64 UNIX, ported to Microsoft Windows and Sun Unix.
Operating system: Tru64 Unix, Microsoft Windows, Sun Unix.
RAM: Case dependent.
Keywords: Ro-vibrational, Bound states, Wavefunctions, Body-fixed, Discrete variable representation, Finite basis representation, Tetraatomic, 4-atom.
PACS: 34.30+h, 33.20-t, 33.20Vq.
Classification: 16.3, 16.2, 16.1.

External routines: LAPACK and BLAS (Can be downloaded from Netlib.org).

Nature of problem:
WAVR4 calculates the bound ro-vibrational levels and wavefunctions of a tetraatomic system using body-fixed coordinates based on generalised orthogonal vectors.

Solution method:
The angular coordinates are treated using a finite basis representation (FBR) based on products of spherical harmonics. A discrete variable representation (DVR) [1] based on either Morse-oscillator-like or spherical-oscillator functions [2] is used for the radial coordinates. Matrix elements are computed using an efficient Gaussian quadrature in the angular coordinates and the DVR approximation in the radial coordinates. The solution of the secular problem is carried through a series of intermediate diagonalisations and truncations.

(1) The size of the final Hamilitonian matrix that can be practically diagonalised.
(2) The DVR approximation for a radial coordinate fails for values of the coordinate near zero - this is remedied only for one radial coordinate by using analytical integration.

Unusual features:
A user-supplied subroutine to evaluate the potential energy is a program requirement.

Running time:
Problem dependent.

[1] J.C. Light, I.P. Hamilton, J.V. Lill, J. Chem. Phys. 92(1985)1400
[2] J.R. Henderson, C.R. Le Sueur, J. Tennyson, Comp. Phys. Comm. 75(1993)379