A High-Precision Calculation of Bond Length and Spectroscopic Constants of Hg₂ Based on the Coupled-Cluster Theory with Spin–Orbit Coupling

Based on the two-component relativistic effective core potential and matched basis sets cc-pwcvnz-pp (n=Q, 5), combining the completed basis-set extrapolation of electronic correlation energy and the fourth-order polynomial fitting technique, the bond length and spectroscopic constants of Hg₂ are studied by the coupled cluster theory with spin–orbit coupling. Spin–orbit coupling is included in the post Hartree–Fock procedure, i.e., in the coupled-cluster iteration, to obtain more reliable theoretical results. The results show that our theoretical values agree with the experimental values very well and will be helpful to understand the spectral character of Hg₂.