Figure 9.

The molecular-orbital states ($|\sigma$ and $\left|{\sigma }^{\ast }\right)$ are related to the energies $E_{\sigma }$ and $E_{{\sigma }^{\ast }}$ are broadening into the valence band and the conduction band when the solid is formed, where, $\eta \left(E\right)$ represents the density of states while $E_g$ represents the band gap energy [44].