Relativistic and non-relativistic electronic molecular-structure calculations for dimers of 4p-, 5p-, and 6p-block elements

摘要

We report results of non-relativistic and two-component relativistic single-reference coupled-cluster with single and double and perturbative triple excitations [CCSD(T)] treatments for the 4p-block dimers Ga_2 to Br_2, the 5p-block dimers In_2 to I_2, and their atoms. Extended basis sets up to pentuple zeta are employed and energies extrapolated to the complete basis-set limit. Relativistic and non-relativistic results for the dissociation energy D_e are in close agreement with each other and previously published data, provided non-relativistic or scalar-relativistic results are corrected for spin-orbit contributions taken from the literature. An exception is Te_2 where theoretical results scatter by 0.085 eV. By virtue of this agreement it is unexpected that comparison with the experimental D_0 or D_e dissociation energies (zero-point vibrational effects are negligible in this context) reveal errors larger than 0.1 eV for Ga_2, Ge_2, and Sb _2. Only relativistic treatments are presented for the 6p-block cases Tl_2 to At_2. Sufficient agreement with experimental data is found only for Pb_2 and Bi_2, the deviation of the computed and experimental D_0 values for Po_2 is again larger than 0.1 eV. Deviations of 0.1 eV between the computed and experimental D_0 values are a major reason for concern and call for additional investigations in both fields to clarify the situation.