Boundary-condition-determined wave function for the ground state of helium and isoelectronic ions

A simple nonvariational wave function for two electron atoms is described. The radial part is derived from the asymptotic one-electron wave functions that are modified to account for the proper core boundary conditions. The electron-electron correlation is described by an ansatz which has the correct behavior for r(12)-->0 and r(12)-->infinity. The additional parameter in this ansatz is calculated from a perturbation calculation. This wave function yields ground-state energies for the heliumlike atoms with Z=1 (H-) to 10 (Ne8+) within 0.0021-0.0068E(h) of the exact energies, which is significantly better than obtained with previous models. We also calculated [r(2n)] and multipolar polarizabilities and performed other tests on this wave function.