Treatment of Degeneracies in the Schrödinger Perturbation Theory by Partitioning Technique

The degenerate case in the Schrödinger perturbation theory has been treated by use of the partitioning technique developed by Löwdin. In order to simplify the concept and treatment, the repeated partitioning technique is utilized. This repeated partitioning allows us to use a one-dimensional reference space and to determine the correct zero-order wavefunction φA.