Ab initio calculations of the atomic and electronic structure of MgF₂ (011) and (111) surfaces

The results of ab initio slab calculations of surface relaxations, rumplings and charge distribution for the different terminations of the MgF₂ (011) and (111) polar surfaces are presented and discussed. We have employed the computer code CRYSTAL with the Gaussian basis set and the hybrid B3PW exchange-correlation functional. Despite the ionic nature of the chemical bonding at both surfaces, a considerable decrease of the optical band gap is predicted (1. 3 eV or 10%) for the (111) surface as compared to the bulk.