Electron correlation and relativistic effects in the secondary NMR isotope shifts of CSe2

Abstract

Secondary isotope effects on nuclear shielding provide an experimentally well-defined reference point of quantum-chemical methodology. We carry out a quantum-mechanical treatment of thermal rovibrational motion in the linear CSe2 molecule and combine it with relativistic modeling of (77)Se and (13)C nuclear magnetic shieldings. The effects of electron correlation are studied at nonrelativistic (NR) ab initio and both NR and relativistic density functional theory (DFT) levels. Fully relativistic 4-component Dirac-DFT (D-DFT) as well as Breit-Pauli perturbation theory (BPPT) are used to produce the relativistic shielding surfaces. Quantitative agreement with the experimental secondary isotope effects can be obtained by a piecewise combination of a high-level ab initio NR shielding surface with the more approximate, albeit reasonable-quality relativistic corrections by DFT at either Dirac or BPPT levels of theory, when operating at the basis-set limit. Using a high-quality potential energy surface is also crucial, which further underlines the highly demanding nature of modeling of the isotope shifts.

Relativistic Heavy-Neighbor-Atom Effects on NMR Shifts: Concepts and Trends Across the Periodic Table

“…Even a relatively “light” HA like sulfur can induce an overall δ SO shielding of −8 ppm at the adjacent 13 C nuclei of CS 2 via the CS double bonds. , In addition to the two factors mentioned above, a large carbon 2s character in the C–S bonds (formal sp 2 hybridization) also aids this shielding. A thorough study of the SO-HALA effects in heavy chalcogen complexes at the Coupled-Cluster with Single and Double and Perturbative Triple excitations CCSD­(T) and Breit-Pauli Perturbation Theory (BPPT) levels of theory was performed to evaluate secondary isotope effects on nuclear shielding in CSe 2 . , …”

Correlated ab initio calculations of one‐bond 31P77Se and 31P125Te spin–spin coupling constants in a series of PSe and PTe systems accounting for relativistic effects (part 2)

“…[61] This idea was successfully applied in calculations of NMR parameters by numerous authors. [62][63][64] We understand that the idea does not reflect the true nature, but our previous calculations of SSCCs involving either selenium nuclei or tellurium nuclei [28,[65][66][67] have also indicated that this assumption leads to satisfactory estimations. To provide a rather reliable description of the electron correlation, we have used, as a starting point, the combination of the SOPPA (CC2) method for the evaluation of 1 J( 77 Se, 31 P) and 1 J( 125 Te, 31 P) SSCCs at the nonrelativistic level of theory and the fourcomponent DFT-KT1 approach for the relativistic corrections.…”

Nuclear‐Spin‐Induced Cotton–Mouton Effect in a Strong External Magnetic Field

“…The reason for such small relativistic effects on the heavy 77 Se nucleus could be in the significant mutual cancellation of the different relativistic influences on the nuclear shielding tensor, which were recently discussed in ref. [49].…”