Current Status of Theory of Nuclear Quadrupole Interaction in Metallic Systems

Abstract

This paper deals with the current status of understanding of the factors that determine the origin of nuclear quadrupole interactions in metallic systems. The major emphasis is on pure metals in which there is currently better understanding of the origin of the electric field gradient (EFG) at the nuclear sites. The procedures for the determination of the electron densities that lead to the electronic contributions to the EFG’s is discussed as well as the quantitative procedures for incorporation of antishielding effects. The nature of agreement between theory and experiment is examined by considering the hexagonal close packed metals beryllium, magnesium, zinc and cadmium. The sensitiveness of the calculated EFG to the procedure used for obtaining electron densities is discussed in beryllium using orthogonalized plane wave and augmented plane wave procedures. The nature of agreement between theory and experiment currently attainable for semi-metals and semiconductors is discussed. The bearing of some of the results in these latter systems by procedures dealing with clusters of atoms to simulate the infinite solid on the future of such procedures for imperfect systems and surfaces is commented upon. A brief discussion is presented about the various possible contributors to the temperature dependence of EFG’s in pure metals and comparison is made between theory and experiment for zinc and cadmium. The factors that can contribute to the EFG’s in imperfect metallic systems, including alloys, at both host and impurity nuclei are discussed, and some of these factors are illustrated by considering two examples of these systems, EFG ’s at host Al and Cu nuclei due to mu mesons introduced in the metal and at impurity nuclei in alloys involving cadmium metal host. The concluding section discusses directions in which further efforts are needed to improve our theoretical understanding of both pure metals and imperfect metallic systems.