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Manuscript Title: Relativistic and non-relativistic configuration interaction calculations for atoms having a closed core and two valence spin- orbitals.
Authors: D.R. Beck, R.N. Zare
Program title: SOCKITTOME 1
Catalogue identifier: AAKA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1969)113
Programming language: Fortran.
Computer: CDC 6400.
Operating system: 6400/6500/6600 SCOPE VERSION 3.1.3.
RAM: 14K words
Word size: 60
Keywords: Atomic physics, Structure, Central field Approximation, Configuration Interaction, Low-z pauli Approximation, Modified Hartree-fock Slater equation, Linear variation Technique, Self-consistent field.
Classification: 2.1.

Nature of problem:
The problem is to obtain wavefunctions for bound atomic levels which permit accurate calculation of energies and transition probabilities. The low-Z Pauli approximation, which is correct to orders Z**3alpha**2 and Z**4alpha**2 in the energy (the non-relativistic energy is of order Z**2) is used to approximate the atomic Hamiltonian. The anti-Hermitian part of those operators characteristic of the Dirac theory is dropped.

Solution method:
The wavefunction is expanded in single configuration functions which are eigenstates of S**2, L**2, J**2, Jz, and parity. All configurations in the expansion must have a closed core and two valence spin-orbitals. The single configuration functions are a linear combination of Slater determinants whose elements are of the central field type. The radial part of the elements is obtained from Lindgren's modification of the Hartree-Fock-Slater equation which is solved using the methods of Herman and Skillman. (Three subprograms were originally written by Herman and Skillman in Fortran II. All statements incompatible with Fortran IV as defined in the Control Data 6400/6500/6600 Computer Systems Manual were altered so as to be compatible with Fortran IV). The coefficients are obtained by application of the variational principle (linear variation technique). The program allows exclusion of any relativistic operators and consequently strictly non-relativistic calculations may also be done.

Restrictions:
The program requires 141 0008 high speed core locations at 60 bits per word. The 32 bits per word of the IBM 360 may not suffice.

Running time:
The running time (all operators) for a test case (Ba I with 6s**2, 6s7s, 6p**2(1S0,3p0), 6p7p, 5d**2, 5d6d configurations for even parity and J= 0) was six minutes on the CDC 6400. A more realistic expansion (one containing 25-30 terms) would take about one hour of CDC 6400 computing time.