Density functional theory is used to investigate the interaction of CO2 with the 100 and 010 surfaces of a Cu(benzene 1,3,5 tricarboxylate) metal organic framework. The calculation method is first validated by applying it to similar systems for which reliable results have been reported in literature and verifying that consistent results are obtained. The method is then applied to the Cu(benzene 1,3,5 tricarboxylate) system. The results show that neither the 100 or 010 surface undergoes major surface relaxation or surface reconstruction during structural optimization. CO2 adsorption calculations show that on the 100 surface, the CO2 molecule interacts with the surface benzene ring through pi-pi interaction. On the 010 surface, the interaction between the CO2 and the surface is again dominated by dispersion. Population analysis shows that a Cu atom on the 010 surface, even when nominally coordinatively unsaturated, is not electron deficient, which explains why CO2 does not bind to it chemically. Adsorption of multiple CO2 molecules on the 100 surface was also studied to investigate the dependence of the interaction on surface coverage. Least squares fitting of experimental adsorption versus pressure data to the BET isotherm model yields a binding energy in good agreement with the first -principles calculations. (C) 2016 Elsevier B.V. All rights reserved.