Theory of magnetic susceptibilities and NMR chemical shifts in terms of localized quantities. II. Application to some simple molecules

Abstract

A coupled Hartree–Fock method with individual gauge for localized orbitals (IGLO) proposed previously is reformulated and applied to the calculation of the magnetic susceptibility χ and the chemical NMR‐shifts σ of various small molecules. The agreement with experiment is usually very good. Unlike in traditional methods, the results are not very sensitive to the size of the basis, and the application to large molecules does not pose serious problems. The results are analyzed in terms of orbital contributions, and it is shown that local diamagnetic terms are transferable, while local paramagnetic as well as nonlocal contributions are not. Pictorial explanations of the large antishielding effects in F₂ and H₂CO are given. In CH⁺₃, a large dependence of χ and σ on changes of the geometry (pyramidalization) is found.