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Manuscript Title: The QB program: analysing resonances using R-matrix theory.
Authors: L. Quigley, K.A. Berrington, J. Pelan
Program title: QB
Catalogue identifier: ADJC_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 114(1998)225
Programming language: Fortran.
Computer: DEC workstation.
Operating system: Unix (HP-UX/ Linux/ Unicos).
RAM: 5M words
Word size: 64
Keywords: Atomic physics, Electron atom, Scattering, Electron ion scattering, Photoionization, Resonance, R-matrix, General purpose, Fit.
Classification: 2.4, 4.9.

Nature of problem:
A procedure for analysing resonances in atomic and molecular collision theory is programmed, which exploits the analytic properties of R-matrix theory to obtain the energy derivative of the reactance (K) matrix and hence the eigenphase sum derivative. Searching for maxima in this gives positions, widths and identifications for all resonances in a given energy range.

Solution method:
This procedure is based on the QB method [2] which defines matrices Q and B in terms of asymptotic solutions, the R-matrix and energy derivatives, such that dK/dE = B**-1Q, from which eigenphase gradients of the K matrix can be obtained. Resonance positions are defined at the points of maximum gradient; resonance widths are related to the inverse of the eigenphase gradients: resonance identifications are estimated from outer region solutions.

The present version is for input specified by the 'H-file' of RMATRX1 [1] and is for ionic targets only; a more appropriate asymptotic program is needed for the case of negative ion resonances.

Running time:
The test run takes 2s on a HP735 workstation.

[1] K.A. Berrington, W.B. Eissner and P.H. Norrington, Comput. Phys. Commun. 92 (1995) 290.
[2] L. Quigley and K.A. Berrington, J. Phys. B: At. Mol. Opt. Phys. 29 (1996) 4529.