Band theory semimetal

Unlike free electron theory, we now have the possibility of completely filled bands and it is the absence of partially filled bands that distinguishes non-metals and semimetals. An electron in a full band cannot be excited to a higher energy level in the same easy way as in a partially filled band sufficient energy must be available to enable the electron to reach a level in the next highest energy band. 

The Fermi surface of CeSb was thus calculated on the basis of p-f mixing theory, although it was not easy. This is because the Ce pnictides are semimetals and their energy band structures and Fermi surfaces are simple. In the usual Ce compounds where the 4f electrons are believed to be localized, it is difficult to carry out such calculations. Therefore, simplified calculations were carried out for such Ce compounds as CeAl2... 

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