Relativistic Electron‐Phonon Interaction. Niobium and Tantalum

The theory of Gaspari and Gyorffy of the electron–phonon interaction is generalized to the relativistic case. Starting from the Dirac equation an expression for the Hopfield parameter η is derived in the rigid muffin‐tin approximation. As an example the Hopfield parameter is calculated for Nb and Ta by the relativistic APW method. The numerical results show that relativistic effects are important in Ta. However the direct influence of spin‐orbit interaction on the electron– phonon interaction is neglegible both, in Nb and Ta.