Relativistic all-electron coupled-cluster calculations on Au2 in the framework of the Douglas–Kroll transformation

We report relativistic all-electron coupled-cluster calculations on the gold dimer, using methods based on the Douglas–Kroll transformation. We use basis sets comprising up to i-type functions and study the dependence of Re, De, and ωe on basis set size, correlation method, and basis set superposition error. It is found that the dispersion interaction (electron correlation) between the gold d shells is described satisfactorily only if basis sets with angular momenta up to at least h functions are used. Mo/ller–Plesset calculations up to fourth order tend to underestimate the bond distance, while averaged coupled-pair functional and coupled-cluster calculations including perturbative triples converge to molecular parameters close to experiment. Correlating the 5p semicore of the gold atoms is found to have a non-negligible contribution.