Pb9Cu(PO4)6O is a charge-transfer semiconductor

By means of density functional theory and constrained random phase approximation we analyze the band structure of ${\mathrm{Pb}}_{9}\mathrm{Cu}{({\mathrm{PO}}_{4})}_{6}\mathrm{O}$ (named LK-99). Our data show that the lead-phosphate apatite LK-99 in the proposed Cu-doped structure is a semiconductor with a predominant charge-transfer nature, a result incompatible with a superconducting behavior. In order to understand the interesting electronic and magnetic properties of this compound, it will be necessary to study the actual response to doping, the possibility of alternative structural and stoichiometric (dis)order, and to clarify the magnetic interactions as well as their impact on the electronic structure.