  By means of density functional theory and constrained random phase
approximation we analyze the bandstructure of Pb$_9$Cu(PO$_4$)$_6$O (named
LK-99). Our data show that the lead-phosphate apatite LK-99 in the proposed
Cu-doped structure is a semiconductor with predominant charge-transfer nature,
a result incompatible with a superconducting behaviour. 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)orders and to clarify the
magnetic interactions as well as their impact on the electronic structure.
