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Manuscript Title: K-matrix calculation for general nonlocal potentials.
Authors: J. Horacek, J. Bok
Program title: CEFEUSK
Catalogue identifier: ABRP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 59(1990)319
Programming language: Fortran.
Computer: IBM-PC/XT/AT.
Operating system: PC (MS) DOS 2.0 OR LATER.
Word size: 16
Keywords: Lippmann Schwinger equation, Scattering solution, K-matrix, Nonlocal interaction, Coordinate space, Iterations, Continued fractions, Atomic physics, Electron, Nuclear physics, Coulomb excitation.
Classification: 2.4, 17.13.

Nature of problem:
The program CEFEUSK calculates the phase shifts (K-matrix) in the coordinate representation for the Lippmann-Schwinger integral equation with a general (local or nonlocal) potential. Unlike the other approaches, the nonlocal part of the potential is not assumed to be separable. The program can be widely applied for any calculation of elastic scattering processes like electron-atom scattering in the static exchange approximation, optical potential calculation etc. An important feature of the program is the high and controlled accuracy. This program can also serve as a very efficient tool for calculation of phase shifts for purely local potentials. In particular, CEFEUSK has been used to solve the electron-hydrogen atom scattering equations.

Solution method:
The algorithm is based on the method of continued fractions (MCF) combined with the Romberg extrapolation technique.

Restrictions:
It is assumed that the interaction potential is given as a sum of a local and a nonlocal potentials. Both potentials are real and the nonlocal one is assumed to be symmetrical. The nonlocal part of the potential need not be separable.

Running time:
The actual running time depends very strongly on the specified input parameters (momentum of the particle, angular momentum, required accuracy). Typical running time on a IBM-PC/AT compatible with 10 MHz CPU 80286/80287 is several tens seconds (100s for test run 1, 60s for test run 2).