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Manuscript Title: Subroutines for the evaluation of exchange integrals in the impact parameter formulation of atomic charge transfer collisions.
Authors: C.J. Noble
Program title: IPEXMAT
Catalogue identifier: ACZU_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 19(1980)327
Programming language: Fortran.
Computer: IBM 370/165.
Operating system: OS/MVT RELEASE 21.7.
RAM: 60K words
Word size: 8
Keywords: Molecular, Integrals exchange, Fourier transform, Impact parameter, Collisions.
Classification: 16.10.

Subprograms used:
Cat Id Title Reference
ACZV_v1_0 REXMAT CPC 19(1980)327

Nature of problem:
A convenient description of atomic charge transfer collisions at moderate and high velocities is provided by the impact parameter formalism. Within this formalism it is advantageous to use a basis consisting of Slater-type orbitals which possess the virtue of having an appropriate asymptotic behaviour. This choice, however, leads to exchange integrals which are difficult to compute rapidly. The present collection of subroutines is designed to compute tables of these one- electron exchange integrals which may be used to obtain the matrix elements required in charge transfer calculations by interpolation.

Solution method:
The exchange matrix elements are evaluated using the Fourier transform reduction method suggested by Sin Fai Lam.

The principal and orbital angular momentum quantum numbers defining the single particle orbitals on each centre are restricted to the ranges n<=12 and l<=12 in the present version of the code. Both restrictions may be relaxed by including further algebraic results.

Unusual features:
The code REXMAT, written in the REDUCE2 language and described in the following program summary, may be used to generate the algebraic results necessary to extend the range of quantum numbers (defining the orbitals on each centre of the exchange integrals) which the code is able to handle.

Running time:
The test run including compilation, required about 5 s on an IBM 370/ 165.