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Manuscript Title: REOS, a program for relaxed-orbital oscillator strength calculations.
Authors: S. Fritzsche, C.F. Fischer
Program title: REOS
Catalogue identifier: ADEJ_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 99(1997)323
Programming language: Fortran.
Computer: IBM RS 6000.
Operating system: IBM AIX 3.2.5+.
RAM: 200K words
Word size: 32
Keywords: Atomic physics, Structure, Determinant, Electron rearrangement, Multiconfiguration, Dirac-fock, Oscillator strength, Relativistic, Transition probability, Spectroscopy.
Classification: 2.1, 2.2.

Subprograms used:
Cat Id Title Reference
ADCB_v1_0 CESD CPC 92(1995)111
ADCU_v1_0 GRASP92 CPC 94(1996)249

Nature of problem:
The separate optimization of a wave function for an atomic state results in a set of electron orbitals which are not quite orthogonal to the orbitals obtained for a different state. In atomic transitions, this incomplete orthogonality reflects the rearrangement of the electron distribution. The REOS program accounts for incomplete orthogonal initial and final states in the calculation of Einstein coefficients, oscillator strengths and radiative lifetimes using relativistic wavefunctions from the GRASP92 package [1] and a representation of the atomic state in a determinant basis.

Solution method:
To compute transition probabilities and lifetimes, REOS applies relativistic wavefunctions from the GRASP92 package [1] and a representation of the atomic state functions |Psi alpha(PJM)>(ASF) in a determinant basis. The expansion of the ASF into determinants can, for instance, be carried out with the CESD program [2]. The formalism of Lowdin [3] is applied to evaluate the radiative transition amplitudes which, as usual, are expressed in terms of multipole fields. In Lowdin's method, the computation of the transition amplitudes requires a summation over all co-factors of the overlap matrix multiplied with associated one-particle matrix elements.

The size of the wave function expansion is the main restriction for the GRASP92 package. In many applications, storage and processing time often provide a basic limitation on the maximal number of configuration state functions. Another limitation of GRASP92 arises from the implemented list of coefficients of fractional parentage to subshells with j <= 7/2; this also restricts the decomposition of configuration state functions (CSF) into determinants.

Unusual features:
The program is designed for interactive use. The computation of only a few selected transitions can be specified by the level numbers of the corresponding initial and final states. As with GRASP92, REOS applies dynamic allocation of the storage as appropriate for the computation with large CSF lists. A few other dimensions which need not be modified in standard applications are defined by PARAMETER statements. No preprocessing of raw code is required.

Running time:
10 seconds on a RS 6000-520.

[1] F.A. Parpia, C.F. Fischer and I.P. Grant, Comput. Phys. Commun. 94(1996)249.
[2] S. Fritzsche and I.P. Grant, Comput. Phys. Commun. 92(1995)111.
[3] P.O. Lowdin, Phys. Rev. 97(1955)1474.