Description of Molecular and Covalent Crystals

A possible application of the idea of mutually consistent group functions is the description of polar molecular crystals. By the virtue of the translational symmetry 

We should be aware of the fact that such a local description does not supply for the correct wave function of the crystal, which ought to respect the translational symmetry. Nevertheless, orbitals localized to the unit cell can be excellent starting points for the construction of a good quality tight-binding wave function of the crystal, either in the framework of a perturbational treatment [154, 155] or using them as basis function to build up Bloch orbitals [156]. 

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