Beschreibung:
<jats:p>A lower-bound procedure for obtaining energy eigenvalues by use of the partitioning technique and bracketing theorem, which have been developed by Löwdin, is extended to the case of a multidimensional reference manifold and is applied to the ground state of the two-electron isoelectronic series. Except for H−, the agreement between upper and lower bounds is quite satisfactory. The process of obtaining lower bounds for excited states is considered.</jats:p>