Density functional theory insulators

Liechtenstein AI, Anisimov VI, Zaanen J (1995) Density-functional theory and strong interactions orbital ordering in Mott-Hubbard insulators. Phys Rev B 52(8) R5467... 

Kudin, K., Scuseria, G., Martin, R. (2002). Hybrid density-functional theory and the insulating gap of UOj. Phys. Rev. Lett. 89,266402. 

Density functional theory is a successful approach for the description of ground-state properties of metals, semiconductors, and insulators. It also has become an attractive method to calculate complex materials, such as proteins and carbon nanotubes. For example, DFT calculation has been used to compute anion-binding properties of 2,6-diamidopyridine dipyrromethane hybrid macrocycles (18), to predict drug resistance of HIV-1 reverse transcriptase to nevirapine through point mutations (19), and to analyze the 32-adrenergic G protein-coupled receptor (20). A free DFT software program also is available... 

Current approximations to density functional theory are not equally successful for all materials. While its formulation is general, there are some materials for which the EDA and GGA do not seem to be adequate. Examples include the transition metal oxides, and presumably transition metal bearing silicates as well. The problem is that the strongly localized Coulomb repulsion between d electrons does not seem to be adequately represented. As a consequence, FeO wustite is predicted to be a metal in LDA and GGA, whereas experimental observations find an insulator. Despite this failure, it is interesting to note that the structural and elastic properties of FeO are well reproduced by LDA (Isaak et al. 1993). In any case, the complete understanding of Mott insulators will require new advances in theory. These will need to go beyond such developments as the LDA+U method which has yielded considerable insight but adds the local Coulomb repulsion (U parameter) in an ad hoc manner (Mazin and Anisimov 1997). 

In contrast, Kulikov (1982) calculates the band structures of LaHj and LaHj, using self-consistent local-density functional theory. He stresses the importance and sensitivity of the choice for the crystal potential, finding incipient overlap between the conduction and valence bands for LaHj. The concept leads to an excitonic insulator phase at low temperatures. The low-temperature phase is semiconducting, and the higher-temperature phase is metallic i.e., the interpretation is opposite from that of Fujimori and Tsuda (1981). 

Extensions of this model in which the atomic nuclei and core electrons are included by representing them by a potential function, V, in Equation (4.1) (plane wave methods) can account for the density of states in Figure 4.3 and can be used for semiconductors and insulators as well. We shall however use a different model to describe these solids, one based on the molecular orbital theory of molecules. We describe this in the next section. We end this section by using our simple model to explain the electrical conductivity of metals. 

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