ABSTRACT
In general terms, there are two approaches to predicting electronic dispersion relations (band structure) of solids: nearly free electron theory and tight-binding theory. In nearly free electron theory, we make the simplifying assumption that the valence electrons are nearly free particles. The effect of the periodic potential due to the ionic cores of the atoms on the electron wave function is small. In tight-binding theory, on the other hand, we assume that the wave function of the electron in the system can be approximated by a linear combination of the wave functions of electrons bound to individual atoms in the system (atomic orbitals), wave functions which overlap by some small amount.
