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 R-e, D-e, and omega(e) 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. Moller-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. (C) 2000 American Institute of Physics. [S0021-9606(00)30904-7].