Global potentials for the interaction between the Ar atom and gold surfaces are investigated and Ar-Au pair potentials suitable for molecular dynamics simulations are derived. Using a periodic plane-wave representation of the electronic wave function, the nonlocal van-der-Waals vdW-DF2 and vdW-OptB86 approaches have been proved to describe better the interaction. These global interaction potentials have been decomposed to produce pair potentials. Then, the pair potentials have been compared with those derived by combining the dispersionless density functional dlDF for the repulsive part with an effective pairwise dispersion interaction. These repulsive potentials have been obtained from the decomposition of the repulsive interaction between the Ar atom and the Au-2 and Au-4 clusters and the dispersion coefficients have been evaluated by means of ab initio calculations on the Ar+Au-2 complex using symmetry adapted perturbation theory. The pair potentials agree very well with those evaluated through periodic vdW-DF2 calculations. For benchmarking purposes, CCSD(T) calculations have also been performed for the ArAu and Ar+Au-2 systems using large basis sets and extrapolations to the complete basis set limit. This work highlights that ab initio calculations using very small surface clusters can be used either as an independent cross-check to compare the performance of state-of-the-art vdW-corrected periodic DFT approaches or, directly, to calculate the pair potentials necessary in further molecular dynamics calculations.