Characterising MgF2 surfaces with CO adsorption calculations

► DFT calculations on the Lewis acidity of unsaturated surface cations of MgF2 crystals ► MgF2 exposes mainly (110), (100) and (101) surfaces with only 5-fold coordinated cations. ► Surfaces that contain also 4-fold coordinated cations - (001) and (111) - are less stable. ► Lewis acidity of 5- and 4-fold coordinated cations is probed by CO adsorption. ► Calculated frequencies give insights into the complex IR pattern of high-surface MgF2.