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Manuscript Title: A program for the calculation of Landau-Zener cross sections and rate coefficients.
Authors: S. Bienstock
Program title: LZRATE
Catalogue identifier: AACJ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 29(1983)333
Programming language: Fortran.
Computer: VAX 11/780.
Operating system: VMS AND MVS.
RAM: 40K words
Word size: 8
Peripherals: disc.
Keywords: Cross sections, Charge exchange, Charge transfer, Expotential integrals, Ionic-covalent Interaction, Ionic recombination, Landau-zener, Mutual neutralization, Scattering, Molecular physics.
Classification: 16.8.

Nature of problem:
The Landau-Zener (LZ) approximation is a widely used procedure for estimating the cross sections and rate coefficients for a number of collision processes which are describable in terms of potential curve crossings. Among them are charge transfer and mutual neutralization. The LZ method has the advantage of requiring only a minimum of information about the physical system under consideration: furthermore calculations are very inexpensive.

Solution method:
Accurate and efficient procedures have been implemented for the calculation of expotential integrals, and of Maxwellian averages of the same. Much of the information required was available in the numerical analysis literature but had not been applied to this problem. The present computer code will calculate LZ cross sections or rates in a few milliseconds of processor time and should run on almost any computer which has a FORTRAN compiler. It was written for atomic physicists or astrophysicists wishing to calculate cross sections or rates at the planning stage of an experiment, or to carry out a survey of a particular class of atomic processes in order to identify which of those would warrant calculation by more elaborate techniques.

Restrictions:
No more than 20 cross sections or rate coefficients can be calculated by the current version in a single run.

Running time:
About 5 ms per cross section on the VAX 11/780 (0.4 ms on the IBM 3033). About twelve times as long for a rate coefficient.