Universality in Materials

The notion of universality for our present purposes can be viewed from several different perspectives. On the one hand, we can speak of the fact that certain features of our models are themselves generic and apply regardless of material specifics. Alternatively, there are certain features of materials themselves that exhibit a certain level of universality. In the present section we wish to comment on both forms of universality. 

From the standpoint of cohesion in solids, we have seen that the Fermi energy 

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