2D periodic ab initio calculations have been performed for H-2 interacting with a temperature-reconstructed MgO(lll) surface, created from a molecular dynamics (MD) simulation at 300 K. The temperature effects involve both a long-time reconstruction of the surface and instantaneous vibrational displacements. Chemisorption energies of similar to 60 mu J/mol were found. Comparisons with adsorption on ideal and relaxed MgO(lll) slabs show that the physi- and chemisorption properties for the H-2/MgO(111) system are very sensitive to small topological details in the surface structure. The large surface reconstruction at 300 K involves drastic changes of the surface＇s adsorption properties. We also find that a low coordination number of the surface ions is not sufficient to make the site attractive for chemisorption.