Stark effect of hydrogenic ions as a test of the indefinite-metric formalism of the eight-component relativistic wave equation for spin- 1 over 2 particles
The study tested a relativistic wave equation's indefinite-metric formalism by calculating first and second-order Stark shifts for hydrogenic ions up to U91+. The results showed that these shifts perfectly match those predicted by the Dirac theory to 45 significant figures, validating the formalism.