HYPERSPHERICAL HARMONICS EXPANSION OF THE GROUND-STATE OF THE PS(-) ION

We have treated the ground state of the positronium negative ion (Ps(- )) by a hyperspherical harmonics expansion method in which the centre of mass motion is properly accounted for. The resulting system of coup led differential equations has been solved by the renormalized Numerov method We find that the convergence in the Binding Energy (BE) with r espect to inclusion of higher hyperspherical partial waves is quite sl ow for this diffuse system. Using our exact numerical results up to a maximum of 28 for the hyper angular momentum quantum number (K-M) in a n extrapolation formula basd on the hyperspherical convergence theorem s, we get the binding energy of the ground state of Ps(-) as 0.261 668 9 au.