Mott-Hubbard criterion

We obviously ignore electron-electron interactions. Later on, some situations in which such interactions will be important, will be briefly considered (see in particular Mott-Hubbard criterion). In these cases the ratio of the interaction energy and 0 is decisive for the strength of the effect. 

This is not necessarily correct for narrow bands. Owing to insufficient overlap, band conduction may be impossible. (Section 2.2.5). Care must be taken to ensure that the p>article distance specified by the Mott-Hubbard criterion [47], is not exceeded, so that delocalization is possible (see Section 2.2.5). 

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