Relativistic heavy-atom effects on heavy-atom nuclear shieldings

P- LANTTO, S. S. GOMEZ, R. H. ROMERO, G. A. AUCAR AND J. VAARA

JOURNAL OF CHEMICAL PHYSICS

AIP

Año: 2006 vol. 125 p. 184113 - 184126

0021-9606

The principal relativistic heavy-atom effects on the nuclear magnetic resonance (NMR) shielding tensor of the heavy atom itself (HAHA effects) are calculated using ab initio methods at the level of the Breit-Pauli Hamiltonian. This is the first systematic study of the main HAHA effects on nuclear shielding and chemical shift by perturbational relativistic approach. The dependence of the HAHA effects on the chemical environment of the heavy atom is investigated for the closed-shell X^{2+}, X^{4+}, XH2, and XH3^{-} (X=Si-Pb) as well as X^{3+}, XH3, and XF3 (X=P-Bi) systems. Fully relativistic Dirac-Hartree-Fock calculations are carried out for comparison. It is necessary in the Breit-Pauli approach to include the second-order magnetic-field-dependent spin-orbit (SO) shielding contribution as it is the lareger SO term in XH3^{-}, XH3, and XF3, and is equally large in XH2 as the conventional, third-order field-independent spin-orbit contribution. Considering the chemical shift, the third-order SO mechanism contributes two-thirds of the difference of ~1500 ppm between BiH3 and BiF3. The second-order SO mechanism and the numerically largest relativistic effects, which arise from the cross-term contribution of the FC hyperfine interaction and the relativistically modified spin-Zeeman interaction (FC/SZ-KE), are isotropic and practically independent of electron correlation effects as well as ...