The binding energy of the ground-state AuCO+ molecule has been systematically investigated using quantum chemical methods such as various density functionals and correlated wave function based approaches like, second order Moller-Plesset perturbation and the coupled cluster ansatz with perturbative treatment of triple excitations, These were combined with a total of 14 relativistic effective core potential/valence and all-electron basis sets of increasing flexibility for gold and CO, respectively, Special emphasis is paid to the role of the basis set superposition error and the relevance of different ways to improve the one particle basis sets, A significant effect on the basis set superposition error is observed in the density functional schemes upon enlarging the valence basis sets,