# One particle in a potential -1/*r* + lambda/*r* (1-exp(-delta *r*))

## Comparison with ionization energy of two-electron ions as a function of
lambda=1/*Z*

Ground state ionization energy (i.e. -*E*) as a function of lambda for delta = 0.88. This value of delta was chosen
in order to reproduce ionization energy for two-electron ion H- (0.0278)
at lambda = 1. The curve appears close to the ionization energy of of helium
isoelectronic sequence (found by summation of 1/*Z*-expansion). So, the potential -1/*r* + lambda/*r* (1-exp(-0.88 *r*)) approximates an effective potential between the loosely bound electron
and the hydrogenic core in H-.

A program

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Designed by A. Sergeev.