Multireference configuration interaction and coupled cluster study of Gold monosulfide (AuS) including spin–orbit coupling

A multireference configuration interaction with the Davidson correction (MRCI + Q) method, including spin–orbit coupling (SOC), was used to calculate the full potential energy curves of the various Ω states of AuS. The spectroscopic constants of the Ω states of AuS were also calculated and compared with the available experimental results. In general, the MRCI + Q+SOC gives qualitatively correct results but does not provide quantitatively accurate results. The unrestricted coupled cluster singles and doubles with perturbative triples (UCCSD(T)) with SOC describe well the molecular properties (bond lengths, vibrational frequencies, and T_e values) of the Ω states. In particular, the bond length of the ground state (Ω = 3/2(²Π_3/2(1)) (2.158 Å) calculated using the UCCSD(T)+SOC is in excellent agreement with the experimental values (2.156 ± 0.002 Å). Both the dynamic electron correlation effect and SOC are crucial to obtain accurate results. We correctly assigned the atomic asymptotes that are correlated with the Ω states and calculated the bond dissociation energies of various Ω states of AuS.