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Manuscript Title: DVR3D: for the fully pointwise calculation of ro-vibrational spectra of triatomic molecules.
Authors: J. Tennyson, J.R. Henderson, N.G. Fulton
Program title: DVR3DRJ
Catalogue identifier: ACNE_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 86(1995)175
Programming language: Fortran.
Computer: CONVEX C3800.
Operating system: UNIX.
Keywords: Molecular physics, Vibrations, Body-fixed, Discrete variable Representation, Coriolis decoupled, Finite elements, Gaussian quadrature, Vectorised.
Classification: 16.3.

Nature of problem:
DVR3DRJ calculates the bound vibrational or Coriolis decoupled ro- vibrational states of a triatomic system in body-fixed Jacobi (scattering) or Radau coordinates coordinates [1,2].

Solution method:
All coordinates are treated in a discrete variable representation (DVR). The angular coordinate uses a DVR based on (associated) Legendre polynomials and the radial coordinates utilise a DVR based on either Morse oscillator-like or spherical oscillator functions. Intermediate diagonalisation and truncation is performed on the hierarchical expression of the Hamiltonian operator to yield the final secular problem. DVR3DRJ provides the vibrational wavefunctions necessary for DIPJ0DVR [3] to calculate vibrational band intensities, ROTLEV3 [4] or ROLEV3B [5] to calculate rotationally excited states, and DIPOLE3 [6] to calculate ro-vibrational transition strengths.

Restrictions:
(1) The size of the final Hamiltonian matrix that can practically be diagonalised. DVR3DRJ 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. (2) The order of integration in the radial coordinates that can be dealt within the machine exponent range. Some adjustment in the code may be necessary when large order Gauss-Laguerre quadrature is used.

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 usually dominated by the final (3D) matrix diagonalisation. A J=0 calculation on the Convex C3800 takes 95 sec for test run 1 and 48 sec for test run 2. These test runs use 25 Mb and 20 Mb scratch disk space respectively.

References:
[1] J.R. Henderson, J. Tennyson and B.T. Sutcliffe, J. Chem. Phys., 98(1993)7191.
[2] N.G. Fulton, Ph.D. Thesis, University of London (1994).
[3] J.R. Henderson, C.R. Le Sueur and J. Tennyson, Comput. Phys. Commun. 75(1993)379.
[4] J. Tennyson, J.R. Henderson and N.G. Fulton, second program, this article (ROTLEV3).
[5] J. Tennyson, J.R. Henderson and N.G. Fulton, third program, this article (ROTLEV3B).
[6] J. Tennyson, J.R. Henderson and N.G. Fulton, fourth program, this article (DIPOLE3).