Two-component calculations for the molecules containing superheavy elements: Spin-orbit effects for (117)H, (113)H, and (113)F

We have calculated bond lengths, harmonic vibrational frequencies, and dissociation energies for (117)H, (113)H, and (113)F using relativistic effective core potentials (RECPs) with one-electron spin-orbit operators at the two-component coupled-cluster levels of theory. It is shown that any reasonable theoretical descriptions of the electronic structures of molecules containing superheavy elements require consideration of relativistic interactions and electron correlations. Comparisons with available all-electron Dirac-Fock (DF) based results indicate that our two-component approaches are very promising tools in the calculations for the molecules containing superheavy elements. The spin-orbit effects calculated from one- and two-component RECPs are in good agreement with those from all-electron Douglas-Kroll and DF results, implying that the potential average scheme is useful for obtaining one- component RECPs even for superheavy elements. Spin-orbit and electron correlation effects are not additive for molecular properties of (117)H, (113)H, and (113)F, but spin-orbit effects are qualitatively similar at all levels of theory considered. Spin-orbit effects contract R-e and increase omega(e) for (113)H and (113)F, whereas they expand R-e and decrease omega(e) for (117)H. Spin-orbit effects decrease D-e for all molecules considered, but the amount of decrease for (113)H and (117)H is substantially smaller than that estimated from the atomic splittings. For (117)H, our best calculations yield 1.983 Angstrom (R-e), 1403 cm(-1) (omega(e)), and 1.60 eV (D-e). (C) 1999 American Institute of Physics. [S0021-9606(99)30418-9].