Electron correlation in He and isoelectronic ions

The implications of the repulsive Coulombic interaction between two electrons are discussed. They lead to a general correlation property of the wavefunction when the two electrons are close to each other. The importance of this property is illustrated by including a simple correlation function in two pedagogically useful model wavefunctions for the ground state and (2p)(2) (3)p state of He and isoelectronic ions. It leads to a significant improvement in the predicted values for the energies and other properties.