1/15/2024 0 Comments Nacl lattice![]() ![]() These theoretical results, however, seem to have been largely overlooked or ignored, possibly because of problems with uniquely assigning charges to ions. performed band structure calculations for NaCl and concluded that the conduction band is actually mainly located on the Cl − ions. Clark 15, 16, de Boer and de Groot 17, 18, as well as Olsson et al. Slater and Shockley 14 suggested a different picture for NaCl, in which the conduction band also has a substantial Cl 4 s character. While this picture has been presented in many text books and publications 1, 8, 9, 10, 11, 12, 13 this view has occasionally been questioned on theoretical grounds. The conduction band is assumed to have mainly alkali character, involving an empty alkali s level outside a full shell. This band is separated from the conduction band by a large gap. The valence band is primarily of halogen p character. There is a large charge transfer from the alkali atoms to the halogen atoms, which become positively and negatively charged ions. In a one-particle picture, all bands are completely full or empty, and Coulomb interactions are less essential. Ionic insulators, e.g., alkali halides, appear to be conceptually simpler. ![]() Coulomb interactions are essential also in this case. The late transition metal oxides are examples of charge transfer insulators, involving the O 2 p band and the, partly filled, transition metal 3 d band. Slater and Mott insulators primarily involve a partly filled band, in which antiferromagnetic or Coulomb interactions open up a gap. One distinguishes between ionic 1, Slater 2, Mott 3 and charge transfer 4, 5, 6, 7 insulators, all involving quite different mechanisms and having different properties. Insulating compounds host a rich and very varied physics. ![]()
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