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Manuscript Title: A multiconfiguration relativistic Dirac-Fock program.
Authors: J.P. Desclaux
Program title: MULTICONFIGURATION DIRAC-FOCK
Catalogue identifier: ACRV_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 9(1975)31
Programming language: Fortran.
Computer: IBM370/155.
Operating system: OS, HASP 3.
RAM: 348K words
Word size: 8
Peripherals: magnetic tape.
Keywords: Atomic physics, Relativistic dirac-fock, Configuration Interaction, Dirac equation, Eigenvalues, Predictor corrector Method, Self-consistent field, Structure.
Classification: 2.1.

Subprograms used:
Cat Id Title Reference
ACRI_v1_0 CFPJJ - CFP IN JJ - COUPLING CPC 4(1972)377
ACWE_v1_0 MCP75 CPC 11(1976)397
AAGD_v2_0 A NEW VERSION OF NJSYM CPC 8(1974)151

Revision history:
Type Tit le Reference
correction 000B CORRECTION 7/12/76 See below
correction 000A CORRECTION 4/01/75 See below

Nature of problem:
The relativistic Dirac-Fock equations, for neutral atoms or ions in a bound state, are solved numerically within the multi-configuration approximation.

Solution method:
The two, first-order coupled Dirac equations are solved by a five-point numerical, corrector-predictor method. The "in-out" method described by Hartree is used. Self consistency is obtained by an iterative process. All the one-electron functions are required to be orthogonal.

Restrictions:
The orthogonality constraint leads to off-diagonal Lagrange multipliers in the Dirac-Fock equations. There are difficulties to solve the equations in the special case of two open shells with the same symmetry and same occupation number. For this situation the multipliers have to be assumed to be zero but then, of course, the wavefunctions are only approximately orthogonal. The interactions between configurations are assumed to be expressed in terms of Fk, Gk and Rk integrals and this assumption precludes the consideration of single excited configurations which are coupled through one-electron operators.

Unusual features:
Three possiblities are provided for the photon charge distribution, namely: 1. point charge; 2. constant charge inside a sphere; 3. Fermi distribution. An analytical approximation of the Thomas-Fermi potential is included in the program deck such that no initial wavefunctions are required to start the iterative process. Nevertheless, in certain cases the Thomas-Fermi potential may be such a poor initial approximation that convergence will not be achieved. In this case it is possible to use either hydrogenic or previously computed functions as initial estimates. As many orbitals as desired may be frozen.

Running time:
The test case consisting of 1. Single configuration ground state of the lithium atom with a Fermi distribution for the nuclear charge; 2. Single configuration ground state of the neon atom with a constant proton charge distribution; 3. Ground state of the nitrogen atom (which involves three configurations in intermediate coupling) with a point charge nucleus; requires 160 s to compile and 270 s to run on the IBM 370/155.

CORRECTION SUMMARY
Manuscript Title: A multiconfiguration relativistic Dirac-Fock program.(C.P.C. 9(1975)31).
Authors: J.P. Desclaux
Program title: 000B CORRECTION 7/12/76
Catalogue identifier: ACRV_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 13(1977)71
Classification: 2.1.

CORRECTION SUMMARY
Manuscript Title: Unpublished correction to a multiconfiguration relativistic DIRAC- FOCK program.
Authors: J.P. Desclaux
Program title: 000A CORRECTION 4/01/75
Catalogue identifier: ACRV_v1_0
Distribution format: gz
Classification: 2.1.