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 Au2 and Au4 clusters and the dispersion coefficients have been evaluated by means of ab initio calculations on the Ar+Au2 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+Au2 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.

Global potentials for the extremely weak interaction between the He atom and gold surfaces are determined from ab initio calculations and validated with experimental-based determinations of well depth values. Dispersionless density functional periodic calculations are combined with effective pairwise functional parameters for the dispersion. These parameters are obtained from time-dependent density functional theory response theory using localized Hartree−Fock orbitals, as applied on He−Au n clusters. This He−Au pairwise potential is used in molecular dynamics simulations of gas−gold surface collisions from which incident and reflected gas atom velocities allow the determination of energy and momentum accommodation coefficients. Boundary quantities such as slip velocity and thermal resistance are not only derived from these coefficients, but also from a new methodology based on a nonparametric kernel, avoiding the atomic description of the gold surface. Similar collision simulations are performed for Ar for comparison. A model of a rough gold surface is also investigated.