Spin-orbit effects in electric field gradients ofalkali metal atoms

Abstract

Spin-orbit effects in electric field gradients (EFG) of alkaliatoms in the 2P3/2 state are investigated bycomparison of correlated (CCSD(T)) four-component Dirac-Fockresults with scalar relativistic Douglas-Kroll calculations.Since the Douglas-Kroll method is based on a unitarytransformation of the full four-component Dirac Hamiltonian toa two-component form the use of the untransformed EFG operatorleads to the well known picture change error. We therefore usethe point charge nuclear quadrupole moment method incombination with the Douglas-Kroll transformation which removespicture-change effects since only Coulomb-type operators are tobe transformed. We find that spin-orbit effects partiallycompensate scalar relativistic effects and are only importantfor the heavier elements Rb and Cs. A comparison to EFGs derivedfrom valence-only ⟨r-3⟩ values shows that Sternheimercorrections are roughly proportional to the dipolepolarizability of the positively charged atom and can becomevery large for the heaviest atom studied, Cs, amounting to 46%of the total EFG.