Relativistic four-component calculations of indirect nuclear spin-spin couplings in MH4 (M=C, Si, Ge, Sn, Pb) and Pb(CH3)(3)H

Relativistic four-component random phase approximation (RPA) calculations o f indirect nuclear spin-spin coupling constants in MH4 (M=C, Si, Ge, Sn, Pb ) and Pb(CH3)(3)H are presented. The need for tight s-functions also in rel ativistic four-component calculations is verified and explained, and the ef fect of omission of (SS-LL) and (SS-SS) two-electron integrals is investiga ted. Already in GeH4 we see a relativistic increase in the coupling constan t by 12%, and for PbH4 the effect is a 156% increase for the one-bond coupl ing. Large relativistic effects are also computed for the two-bonds couplin gs. We find that the relativistic effects on the one-bond couplings are mai nly due to scalar relativistic factors rather than spin-orbit corrections. (C) 2000 American Institute of Physics. [S0021-9606(00)30408-1].