ABSTRACT
We present fully numerical electronic structure calculations on diatomic molecules exposed to an external magnetic field at the unrestricted Hartree–Fock limit, using a modified version of a recently developed finite-element programme, HelFEM. We have performed benchmark calculations on a few low-lying states of H, HeH
, LiH, BeH
, BH and CH
as a function of the strength of an external magnetic field parallel to the molecular axis. The employed magnetic fields are in the range of
atomic units, where
T. We have compared the results of the fully numerical calculations to ones obtained with the LONDON code using a large uncontracted gauge-including Cartesian Gaussian (GICG) basis set with exponents adopted from the Dunning aug-cc-pVTZ basis set. By comparison to the fully numerical results, we find that the basis set truncation error (BSTE) in the GICG basis is of the order of 1 kcal/mol at zero field, that the BSTE grows rapidly in increasing magnetic field strength, and that the largest BSTE at
exceeds 1000 kcal/mol. Studies in larger Gaussian-basis sets suggest that reliable results can be obtained in GICG basis sets at fields stronger than
, provided that enough higher-angular-momentum functions are included in the basis.
GRAPHICAL ABSTRACT
![](/cms/asset/8d27eb4b-efd1-4311-9ea2-eb797d70cc5a/tmph_a_1597989_uf0001_oc.jpg)
Acknowledgments
We thank Trygve Helgaker and Erik Tellgren for a copy of the London code, and Stella Stopkowicz and Florian Hampe for their tool for determining orbital symmetry.
Disclosure statement
No potential conflict of interest was reported by the authors.