Electronic structure of the putative room-temperature superconductor Pb9Cu( PO4)6O

A recent paper [Lee et al., J. Kor. Cryst. Growth Cryst. Technol. 33, 61 (2023)] provides some experimental indications that Pb10-xCux(PO4)(6)O with x approximate to 1, coined LK-99, might be a room-temperature superconductor at ambient pressure. Our density-functional theory (DFT) calculations show lattice parameters and a volume contraction with x, very similar to experiment. The DFT electronic structure shows Cu2+ in a 3d(9) configuration with two flat Cu bands crossing the Fermi energy. This puts Pb9Cu(PO4)(6)O in an ultracorrelated regime and suggests that, without doping, it is a Mott or charge-transfer insulator. If doped, such an electronic structure might support flat-band superconductivity or a correlation-enhanced electron-phonon mechanism, whereas a diamagnet without superconductivity appears to be rather at odds with our results.