Band theory 2

At T = 0, electrons occupy the energy band in accordance with the building up principle. For example, if each atom donates a single s electron, the band will be half filled:

The highest occupied orbital is called the fermi level.

The density of molecular orbitals is not uniform throughout the band. There is only one way of arranging a purely bonding or purely antibonding orbital, but multiple ways of arranging in-between states. The image below shows density on the x axis:

So more MOs are found in the middle of the bands than on the edges.