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Manuscript Title: RELCI: a program for relativistic configuration interaction calculations.
Authors: S. Fritzsche, C.F. Fischer, G. Gaigalas
Program title: RELCI
Catalogue identifier: ADQH_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 148(2002)103
Programming language: Fortran.
Computer: IBM RS 6000, PC Pentium III.
Operating system: IBM AIX 4.1.2+, Linux 6.1.+.
Word size: 64
Peripherals: disc.
Keywords: Atomic physics, Breit interaction, Configuration interaction, Dirac-Coulomb-Breit Hamiltonian, Large-scale computations, Multiconfiguration Dirac-Fock, QED estimate, Relativistic, Transverse interaction, Structure.
Classification: 2.1.

Subprograms used:
Cat Id Title Reference
ADCU_v1_0 GRASP92 CPC 94(1996)249

Nature of problem:
Approximate atomic wave functions are determined by diagonalizing the Hamiltonian matrix within an appropriate many-particle basis. Here, the construction of the configuration interaction (CI) basis follows the same principles as in the structure code GRASP92 [1] which is utilized to generate the configuration state functions (CSF) and the radial orbitals for all subshells of the given active space.

The size of useful CI expansions critically depends on the shell structure of the atom or ion under consideration. Wave function expansions of several ten (or even hundred) thousand CSF are currently feasible on standard PCs. For more than two equivalent electrons, antisymmetrized subshell states are supported only for j <= 9/2 (i.e. for all shells up to the g9/2 or h9/2 subshells).

Unusual features:
RELCI is designed as part of the RATIP package [2,3] for the calculation of relativistic atomic transition and ionization properties. An interactive dialog at the beginning of the execution enables the user to specify the (relativistic) interactions among the electrons and the mode of computation. A number of different modes are supported with regard to the re-use and maintenance of the internal storage. While the implementation of the program follows lines similar to GRASP92, still, the RELCI program has been rewritten entirely to conform to the new Fortran 90/95 standard [4] and to meet the requirements of modern applications. By using a dynamic allocation of all important arrays, there are no restrictions any more with regard to the numbers of open shells (within a single CSF) or individual subshells. When compared with RCI92 for their run-time behaviour, our new RELCI program is faster by a factor between 3 ... 8, depending on the particular application.

Additional comments:
Memory required Memory requirements strongly depend on the size of the Hamiltonian matrix and the selected mode of computation.
Number of bits in a word All real variables are parametrized by a 'selected kind parameter' and, thus, can easily be adapted to any required precision as supported by the compiler. Presently, the 'kind' parameter is set to double precision (two 32-bit words) in the module 'rabs_constant'.

Running time:
8 minutes on a 550 MHz Pentium III processor.

[1] F.A. Parpia, C.F. Fischer, and I.P. Grant, Comput. Phys. Commun. 94 (1996) 249.
[2] S. Fritzsche, J. Elec. Spec. Rel. Phen. 114-116 (2001) 1155.
[3] S. Fritzsche, C.F. Fischer, and C.Z. Dong, Comput. Phys. Commun. 124 (2000) 343.
[4] M. Metcalf and J. Reid, Fortran 90/95 Explained (Oxford University Press, 1996).