Periodic density functional theory calculations were performed to investigate the Lewis acidity of unsaturated surface cations of ZnF2, using CO as probe molecule at different coverages. We have calculated adsorption energies for CO on all low index ZnF2 surfaces using DFT with the B3LYP functional and subsequent dispersion correction. Additionally local second order Møller-Plesset perturbation theory (LMP2) calculations were performed. In most of the cases, the adsorption of CO on different surfaces is described well using B3LYP. Dispersion correction to B3LYP is found to overestimate the adsorption energy. The interaction among adsorbed CO molecules appears to have a significant effect on the adsorption energies at full coverage.