Sixth-order Douglas-Kroll: two-component reference data for one-electron ions from 1s12 through 4f72

Quasirelativistic Douglas-Kroll calculations including spin-orbit interaction have been performed for hydrogen-like (one-electron) ions. The Douglas-Kroll operators have been implemented up to the sixth order, and a huge even-tempered basis set has been applied that gives results to microhartree accuracy for the energy levels 1s12 through 4f72 for all ions with nuclear charge from Z = 1 up to Z = 100. Besides providing reference data for other implementations, these results can be used to analyse the performance of the Douglas-Kroll method. Such an analysis is presented for the 1s energy levels and the spin-orbit splitting of the 2p shell. The leading order of the error of the Douglas-Kroll result is different for 2s and 2p12 although these levels are degenerate both at nonrelativistic and Dirac level.