Relativistic effects in nuclear quadrupole coupling

Relativistic effects strongly influence the nuclear quadrupole coupling of atoms, molecules or solids. As first shown by Casimir in 1936, in the atomic or single-centre case, for the two states j=l+/-s, three radial electric-field-gradient (EFG) integrals, R++,R+-, and R--, must be introduced. The relativistic correction factors? defined for operator (q) over cap as C = [R\(q) over cap\R]/[NR\(q) over cap\NR], have quite different values for the three combinations. For example. for the Bi atom ground state 6p shell at Dirac-Fock(DF) level, C++ and C+- are 1.28 and 1.91, respectively, while q(--) vanishes entirely, due to j=1/2. There also is a dependence on the n quantum number. In addition to these relativistic changes of the integrals (at the atomic centre), spin-orbit tilting effects may occur, even at light atoms, bonded to heavy ones. We have produced DF-level, EFG integrals for the elements 1-93, investigated the hydrogen-like, n-dependent correction factors, C and used simple molecular-orbital models for estimating the spin-orbit tilting effects.