Calculation of the fourth-rank nuclear magnetic hypershielding of some small molecules

A computational scheme has been implemented to evaluate magnetic hypershielding at the nuclei of a molecule in the presence of an external spatially uniform, time-independent magnetic field, accounting for cubic response contributions via Rayleigh-Schr\"odinger perturbation theory. Numerical estimates have been obtained for hydrogen and heavier atoms in H₂, HF, H₂O, NH₃, and CH₄ molecules at the coupled Hartree-Fock level of accuracy within the conventional common-origin approach. Gaugeless basis sets of increasing size and flexibility have been employed in a numerical test, to estimate the degree of convergence of theoretical tensor components. A further test for convergence has been carried out by evaluating properties for two different coordinate systems.