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Manuscript Title: A general program to calculate atomic continuum processes using the R- matrix method.
Authors: K.A. Berrington, P.G. Burke, J.J. Chang, A.T. Chivers, W.D. Robb, K.T. Taylor
Program title: RMATRX STG2
Catalogue identifier: AAHB_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 8(1974)149
Programming language: Fortran.
Computer: ICL 1906A.
Operating system: GEORGE 4.
RAM: 96K words
Word size: 24
Peripherals: disc.
Keywords: Atomic physics, Electron-atom scattering, Electron-ion scattering, Photoionization, Polarizability, R-matrix, Hamiltonian matrix, Ionic, Racah coefficient, Fractional parentage Coefficient, Recoupling, Angular integral, Continuum, Bound, Ls coupling, Long range potentials, Dipole matrix elements, Scattering, Photon.
Classification: 2.4, 2.5.

Subprograms used:
Cat Id Title Reference
ACQC_v2_0 A NEW D SHELL C.F.P. CPC 6(1973)88
ACQB_v1_0 P SHELL C.F.P. CPC 1(1969)15
ACQL_v2_0 WEIGHTS NEW VERSION CPC 2(1971)180
ACQL_v2_0 0001 ADAPT WEIGHTS FOR ONE-ELECT CPC 7(1974)318
AAGD_v2_0 A NEW VERSION OF NJSYM CPC 8(1974)151
AAKF_v1_0 REDUCED TENSOR MATRIX ELEMENTS CPC 6(1973)132
AAHA_v1_0 RMATRX STG1 CPC 8(1974)149
AAHC_v1_0 RMATRX STG3 CPC 8(1974)150
ACRK_v1_0 ASYM VERSION FOR ICL 1900 CPC 5(1973)416

Other versions:
Cat Id Title Reference
AAHG_v1_0 A NEW VERSION OF RMATRX STG2 CPC 14(1978)367
AANS_v1_0 RMATRX STG2R CPC 25(1982)347

Nature of problem:
This program reads the radial integrals stored on a permanent tape or disc file by RMATRX STG1. It then calculates the hamiltonian matrix elements, the asymptotic potential coefficients and the dipole length and velocity matrix elements from a given initial state to the final state specified by LS and the channel quantum numbers. These quantities are stored on a permanent tape or disc file for use by RMATRX STG3.

Solution method:
The triangular relations are used to deternmine the number of coupled channels given the value of L and S and the quantum numbers of the atomic states. The angular integrals are carried out using the methods of Racah algebra. These are then combined with the radial integrals evaluated by RMATRX STG1.

Restrictions:
Up to 20 continuum orbitals for each angular momentum can be included. This number can be increased by recompiling. The program assumes that L and S are good quantum numbers and neglects effects due to the spinn- orbit interaction.

Running time:
The running time depends on the square of the number of shells and the number of configurations included but in general a single run of STG2 is usually an order of magnitude or more shorter than the STG1 run. The test run took 25 s on the ICL 1906A.