Rutile molecular model and its EUC determination by PM7.

Rutile surface has been modeled in order to study its electronic properties as well as to determine its surface chemical reactivity. There have been constructed 10 different rutile structures, from a 6 atoms cluster (for the smallest) to a 356 atoms cluster (for the biggest). It was calculated for each cluster some physical parameters which are related to the electronic properties, such as work function, band gap, and density of states (DOS), in order to analyze the tendency of the cluster properties with the increase of atoms. From the data obtained, it was determined the Electronic Unit Cell (EUC), which refers to the modeled structure for what the electronic and reactivity properties of the system does no change, from clusters with different number of atoms. From the rutile EUC cluster it was determined its band gap with a value of 3.28 eV, which agreed with the experimental value of 3.0-3.1 eV. Furthermore, it was performed a reactivity surface study, which comprised the analysis of reactivity descriptors such as ionization potential, electronic affinity, total hardness, electronic chemical potential, electrophilicity and electronegativity. All theoretical calculations were performed using the semiempirical PM7 included in the 2012 version of MOPAC and the surfaces were modeled from crystallographic data.