Fig. 5. Simple systems with band gaps induced by local order.

a Square system of s orbitals with different types of hopping parameters forming partial and full dimers, and their corresponding electronic band structures. b Density of states for the square system. c Triangular system of s orbitals from two types of atoms and corresponding electronic bands. d Density of states showing that half filling gives a Fermi level in the band gap induced by hidden order.