Relativistic Effects in the Cohesive Energies of the Alkali Metals

The relativistic corrections to the cohesive energies of the alkali metals are studied from two points of view. In the first, perturbation theory is applied to the second approximation to the Dirac equation. Calculations are made for potassium and cesium. The limitations of this approach are discussed. In the second, the quantum defect method is extended to include almost all relativistic effects. A relativistic analog of Bardeen's expression for the effective mass ratio is derived. Application is made to cesium.