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Manuscript Title: Computation of wavefunctions for the helium isoelectronic sequence.
Authors: H.O. Knox
Program title: TWO ELECTRON WAVEFUNCTIONS
Catalogue identifier: ACQK_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1970)167
Programming language: Fortran.
Computer: ICL 1907.
Operating system: QUBE.
RAM: 20K words
Word size: 24
Peripherals: magnetic tape.
Keywords: Atomic physics, Wave functions, Helium Isoelectronic Sequence, Sturmian functions, Configuration Interaction, Inverse iteration, Eigenvalues, Bound state, Schrodinger equation, Autoionizing state, Resonance, Energy level.
Classification: 2.7.

Nature of problem:
This program computes wavefunctions and energies of the helium isoelectronic sequence to any desired accuracy. The wavefunctions have the correct asymptotic form and therefore they are particularly suitable for use in scattering problems. They have been used to calculate line strengths by Knox and Rudge.

Restrictions:
The size of the wavefunction is limited by the storage available and by rounding errors in the calculation of the matrix elements and in matrix inversion. The major storage requirement is for four matrices whose dimension equals the number of basis functions used; the matrix elements become inaccurate if n1,n2 > 10; and it is not recommended that the present matrix inversion routine be used on matrices larger than 60 X60.

Running time:
The time required to compute one energy and wavefunction increases roughly as N**2 where N is the number of basis functions used and for N=10 it is about 22 seconds on an ICL 1907. The time needed for different wavefunctions of the same size may vary considerably due to the use of an iterative routine.