A simple parameter-free wavefunction for the ground state of two-electron atoms

We propose a simple and pedagogical wavefunction for the ground state of two-electron atoms which (i) is parameter free, (ii) satisfies all two-particle cusp conditions, (iii) yields reasonable ground-state energies, including the prediction of a bound state for H-. The mean energy, and other mean physical quantities, is evaluated analytically. The simplicity of the result can be useful as an easy-to-use wavefunction when testing collision models.