Relativistic study of nuclear magnetic shielding constants: Tungsten hexahalides and tetraoxide

Relativistic ab initio calculations of the W-183 magnetic shielding constant and the chemical shift of WX(6) (X = F and Cl) and WO42- are presented. The computational method is a combination of the relativistic spin-free no-pair theory and the spin-orbit unrestricted Hartree-Fock method, which has been applied previously to Hg-199 magnetic shielding constants. The spin-free relativistic (SFR) terms, involving the mass velocity and Darwin terms, are shown to be important for W-183 shielding constants. The spin-orbit interaction, which is smaller than the SFR term, works differently on WCl6 and WO42-. The effects of relaxing the inner s and p orbitals of W are investigated.