Pseudopotential study of lanthanum and lutetium dimers

Relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart-Bonn variety and extended valence basis sets have been used for the investigation of the dimers La-2 and Lu-2. It was found that the ground states for La-2 and Lu-2 are most likely (1)Sigma(g)+ (sigma(g)(2)pi(u)(4)) and (3)Sigma(g)(-) (4(f)(14)4f(14)sigma(g)(2)sigma(u)(2)pi(u)(2)), respectively. The molecular constants including error bars were derived from multireference configuration interaction as well as coupled-cluster calculations, taking into account corrections for atomic spin-orbit splitting as well as possible basis set superposition errors. The theoretical values for La-2 (R-e = 2.70 +/- 0.03 Angstrom, D-e = 2.31 +/- 0.13 eV, omega(e) = 186 +/- 13 cm(-1)) show good agreement with the experimental binding energy (D-e = 2.52 +/- 0.22 eV), but the experimental vibrational constant in an Ar matrix (omega(3) = 236 +/- 0.8 cm(-1)) is significantly higher. For Lu-2 the theoretical values (R-e = 3.07 +/- 0.03 Angstrom, D-e = 1.40 +/- 0.12 eV, omega(e) = 123 +/- 1 cm(-1)) are in overall excellent agreement with experimental data (D-e = 1.43 +/- 0.34 eV, omega(e) = 122 +/- 1 cm(-1)). The electronic structures of La-2 and Lu-2 are compared to those other lanthanide dimers and trends in the series are discussed.