Gauge origin independent calculations of nuclear magnetic shieldingsin relativistic four-component theory

摘要

The use of perturbation-dependent London atomic orbitals, also called gauge including atomicorbitals, has proven efficient for calculations of NMR shielding constants and other magneticproperties in the nonrelativistic framework. In this paper, the theory of London atomic orbitals forNMR shieldings is extended to the four-component relativistic framework and our implementationis described. The relevance of London atomic orbitals in four-component calculations as well ascomputational aspects are illustrated with test calculations on hydrogen iodide. We find that the useof London atomic orbitals is an efficient method for reliable calculations of NMR shieldingconstants with standard basis sets, also for four-component calculations with spin-orbit couplingeffects included in the wave function optimization. Furthermore, we find that it is important that thesmall component basis functions fulfill the magnetic balance for accurate description of thediamagnetic shielding and that the role of London atomic orbitals in the relativistic domain is toprovide atomic magnetic balance even in the molecular case, thus greatly improving basis setconvergence. The Sternheim approximation, which calculates the diamagnetic contribution as anexpectation value, leads to significant errors and is not recommended.