Relativistically parameterized extended Hückel calculations. VII. Nuclear spin—spin coupling tensors and densities of states for cluster models of CdTe, HgTe and PbTe

Abstract

Relativistically parameterized extended Hückel (REX) calculations of spin—spin coupling tensors 1J(MTe) for cluster models of CdTe, HgTe and PbTe are reported. The relativistic equivalent of Ramsey's theory is used. Electronic densities of states are obtained as a by-product. Two assignments of the experimental NMR data are shown to be possible. The REX results support the original Nolle one for PbTe and the alternative ones for CdTe and HgTe. The increase of Δ J is attributed to relativistic effects, arising from the M( ns)—Te(5p 1 2 ) AO combination, recently discussed by Pyykkö and Wiesenfeld. A principle is proposed that both K and Δ K are positive for systems with dominant bonding-to-antibonding excitations, a case likely for half-filled valence shells. Nearly empty or nearly full valence shells with dominant bonding-to-bonding or antibonding-to-antibonding excitations should lead to negative K and Δ K. Double-zeta REX radial parameters are reported for ZnHg and OPo.