Cluster surface states for TiO2, SrTiO3, and BaTiO3

The properties of cluster surface states of the transition-metal oxides TiO₂, SrTiO₃, and BaTiO₃ are derived from an empirical molecular-orbital model. The relation between cluster states and bulk and surface energy bands is discussed. The possible role of surface states in producing the 2.0-eV peak observed in the electron energy-loss spectrum of TiO₂ and Ti₂O₃ is suggested. Some comments on the use of a cluster model for the interpretation of optical properties are also included.