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Manuscript Title: ATOMDIAT: a program for calculating variationally exact ro- vibrational levels of "floppy" triatomics.
Authors: J. Tennyson
Program title: ATOMDIAT
Catalogue identifier: ACEN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 29(1983)307
Programming language: Fortran.
Computer: IBM 4341/2.
Operating system: MVS RELEASE 3.7.
Program overlaid: yes
Word size: 8
Peripherals: disc.
Keywords: Molecular physics, Vibration, Ro-vibrational, Body-fixed, Associated laguerre Polynomials, Associated legendre Polynomials, Gauss-laguerre Quadrature, Orthogonalised lanczos, Lc-ramp, Variational, Close-coupled equations.
Classification: 16.3.

Revision history:
Type Tit le Reference
adaptation 0001ATOMDIAT2 See below
adaptation 0002GENPOT See below

Nature of problem:
ATOMDIAT calculates the bound ro-vibrational levels of a triatomic system using body-fixed coordinates. The embedded coordinates are appropriate to atom-diatom systems and the diatom bondlength may be frozen.

Solution method:
A basis set is constructed as the product of Morse oscillator functions (associated Laguerre polynomials) for the radial coordinate(s) and associated Legendre polynomials for the bending coordinate, with rotation matrices representing the rotations. The method is variational and the parameters used in constructing the radial basis set(s) can be optimized. A secular matrix is constructed by use of Gauss-Laguerre integration for the radial coordinate(s) and analytic integration for the angular coordinates. This matrix is diagonalised to give the solutions. A choice of Givens-Householder and orthogonalised Lanczos procedures are supplied with the program.

Restrictions:
The size of matrix that can practically be diagonalised. The program allocates arrays dynamically at execution time and in the present version the total space available is a single parameter which can be set as required.

Unusual features:
A user supplied subroutine containing the potential energy as an (analytic) Lengendre polynomial expansion is a program requirement.

Running time:
Running times are case dependent but dominated by the time required for diagonalising the secular matrix. A problem with 350 basis functions (which can be held in 512K) takes 7 min on the IBM 4341/2.

ADAPTATION SUMMARY
Manuscript Title: ATOMDIAT2 and GENPOT: adaptations of ATOMDIAT for the ro-vibrational levels of any floppy triatomic using a general potential function.
Authors: J. Tennyson
Program title: 0001ATOMDIAT2
Catalogue identifier: ACEN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 32(1984)109
Programming language: Fortran.
Computer: NAS 7000.
Word size: 8
Classification: 16.3.

Nature of problem:
ATOMDIAT2 solves the ro-vibrational problem for an atom (1) - diatom system (2-3) for which the linear 213 structure is significant.

Solution method:
Spherical oscillator-like functions are used for the R-coordinate basis. An option allowing the problem to be embedded along r is also included.

ADAPTATION SUMMARY
Manuscript Title: ATOMDIAT2 and genpot: adaptations of atomdiat for the ro-vibrational levels of any floppy triatomic using a general potential function.
Authors: J. Tennyson
Program title: 0002GENPOT
Catalogue identifier: ACEN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 32(1984)109
Programming language: Fortran.
Computer: NAS 7000.
Word size: 8
Classification: 16.3.

Nature of problem:
GENPOT generalises ATOMDIAT or ATOMDIAT2 so that the ro-vibrational states may be obtained for any triatomic potential function, not just one fitted in Legendre polynomials. It can also be used to perform shifts of a potential fitted as a Legendre expansion caused by isotopic substitution.

Solution method:
GENPOT uses Gauss-Legendre quadrature to obtain a Legendre expansion for each R and r.