Figure 9.

Calculated formation energy of V_OH in HAP as a function of the Fermi energy, using different approximations to the DFT exchange–correlation interactions. Positive, neutral, and negative charge states are represented by lines with positive, zero, and negative slope, respectively. For each functional, the Fermi energy can vary between the valence band top (at E_F = 0 eV) and the respective conduction band minimum (E_F = Eg). (Adapted with permission from ref. [11]; AIP Publishing, 2015).