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Manuscript Title: A program for generating complete active spaces for relativistic atomic structure calculations.
Authors: F.A. Parpia, W.P. Wijesundera, I.P. Grant
Program title: JJCAS
Catalogue identifier: ACNG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 76(1993)127
Programming language: Fortran.
Computer: VAX 8700/8800 Cluster.
Operating system: Digital VAX/VMS, Cray UNICOS.
RAM: 14K words
Word size: 32
Peripherals: disc.
Keywords: Atomic physics, Structure, Active space, Configuration, Jj coupling, Relativistic.
Classification: 2.1.

Nature of problem:
Generation of complete active spaces [1,2] in the jj-coupling scheme for models of atomic electronic structure.

Solution method:
The N electrons that constitute the system are distributed in all possible ways in the given set of subshells {nlj} or {nK}. Distributions that violate the upper limits on subshell occupation and distributions with incorrect parity are rejected. All possible angular momentum couplings of the subshells are then generated. Couplings that do not yield the required total angular momentum are rejected. The remainder constitute the complete active space.

Unusual features:
The number of subshells is restricted only by the dimensions set by the user and so ultimately by the available memory and CPU time. In addition to its standard output, JJCAS will generate the complete active space information in a form suitable for input to the Oxford multiconfiguration Dirac-Fock packages [3,4,5,6]

Running time:
Test case 1: 0.39 seconds (VAX), 0.008 seconds (XMP); test case 2: 0.39 seconds (VAX), 0.026 seconds (XMP); otherwise depends on the case and the computer employed.

References:
[1] K. Ruedenberg and K. Sundberg in Quantum Science: Methods and Structure; A Tribute to P.-O. Lowdin, edited by J.-L. Calasi, O. Goscinski, J. Linderberg and Y. Ohrn (Plenum, New York, 1976)
[2] B.O. Roos, P.R. Taylor and P.E.M. Siegbahn, Chem. Phys. 48(1980)157
[3] I.P. Grant, B.J. McKenzie, P.H. Norrington, D.F. Mayers and N.C. Pyper, Comp. Phys. Commun. 21(1980)207
[4] B.J. McKenzie, I.P. Grant and P.H. Norrington, Comp. Phys. Commun. 21(1980)233
[5] K.G. Dyall, I.P. Grant, C.T. Johnson, F.A. Parpia and E.P. Plummer, Comp. Phys. Commun. 55(1989)425
[6] F.A. Parpia, I.P. Grant and C.F. Fischer, 1990, the GRASP program is available from these authors upon application.