The UKB prescription and the heavy atom effects on the nuclear magnetic shielding of vicinal heavy atoms

Abstract

Fully relativistic calculations of NMR magnetic shielding on XYH3 (X = C, Si, Ge and Sn; Y = Br, I), XHn (n = 1-4) molecular systems and noble gases performed with a fully relativistic polarization propagator formalism at the RPA level of approach are presented. The rate of convergence (size of basis set and time involved) for calculations with both kinetic balance prescriptions, RKB and UKB, were investigated. Calculations with UKB makes it feasible to obtain reliable results for two or more heavy-atom-containing molecules. For such XYH3 systems, the influence of heavy vicinal halogen atoms on sigma(X) is such that heavy atom effects on heavy atoms (vicinal plus their own effects or HAVHA + HAHA effects) amount to 30.50% for X = Sn and Y = I; being the HAHA effect of the order of 25%. So the vicinal effect alone is of the order of 5.5%. The vicinal heavy atom effect on light atoms (HALA effect) is of the order of 28% for X = C and Y = I. A similar behaviour, but of opposite sign, is observed for sigma(Y) for which sigmaR-NR (I; X = C) (HAHA effect) is around 27% and sigmaR-NR(I; X = Sn) (HAVHA + HAHA effects) is close to 21%. Its electronic origin is paramagnetic for halogen atoms but both dia- and paramagnetic for central atoms. The effect on two bond distant hydrogen atoms is such that the largest variation of sigma(H) within the same family of XYH3 molecules appears for X = Si and Y = I: around 20%. In this case sigma(H; X = Sn, Y = I) = 33.45 ppm and sigma(H; X = Sn, Y = H) = 27.82 ppm.

Nuclear spin-spin coupling in a van der Waals-bonded system: Xenon dimer

“…Enhanced basis-set convergence for magnetic properties has been reported by this method as compared to the restricted kinetic balance method that leads to a more compact small-component basis. 22,[43][44][45] Similar improvements have recently been reported by the economic simple magnetic balance approach. 46 …”

Four-component relativistic theory for nuclear magnetic shielding: Magnetically balanced gauge-including atomic orbitals

“…Even so, the CP-DHF-type calculations have invoked a diagonal approximation to the orbital Hessian and sizable discrepancies still exist among the results for systems as simple as hydrogen halides. 24,25 This clearly reflects the importance of "finding out" the relativistic diamagnetism so as to guarantee the correct nrl.…”

“…As such, except for some benchmark results for closed-shell atoms/ions at the Dirac-Slater or the coupled-perturbed Dirac-Hartree-Fock ͑CP-DHF͒ level, 1-3,10,11 most of the four-component relativistic calculations on molecular systems [12][13][14][15][16][17][18][19][20][21] suffer from severe basis set incompleteness errors and/or the use of crude approximations for the contributions of NES. 22 As a matter of fact, very few solid CP-DHF [23][24][25] or coupled-perturbed Dirac-Kohn-Sham ͑CP-DKS͒-type 26 molecular calculations have been carried out up to date. Even so, the CP-DHF-type calculations have invoked a diagonal approximation to the orbital Hessian and sizable discrepancies still exist among the results for systems as simple as hydrogen halides.…”

Relativistic and Electron-Correlation Effects on the Nuclear Magnetic Resonance Shieldings of Molecules Containing Tin and Lead Atoms

“…33 The basis sets used were the same that were used in previous works. 12,34,75 Again, Sadlej's basis sets were chosen for all cases 73 except for Pb atom where The whole basis sets with all previous considerations and all geometrical parameters used in calculations are given as Supporting Information.…”

“…We consider as vicinal two atoms that are connected by one bond. 33,34 There are other two relativistic effects on shieldings which are related with electronic effects due to the presence of heavy atoms: i) a heavy atom (relativistic) effect on a vicinal light atom, coined HALA, 63,64 and ii) a heavy-atom effect on the heavy-atom itself, coined HAHA. 65 The first effect is mostly due to spin-orbit interactions, and the second one do contain few new mechanisms that involve the electronic behaviour of core electrons.…”