  The copper substituted Pb-apatite has attracted a great deal of attention
recently, due to the claim of the observation of room temperature
superconductivity. Based on LDA calculations in the literature, we propose an
effective model that describe the low energy physics. It consists of stacks of
buckled honeycomb lattices, with Cu and O occupying the A and B sites
respectively. In addition to the narrow Cu bands that have been emphasized, we
call attention to the relatively small energy separation between the Cu and O
orbitals. Thus despite the small hoping energies, the model may be in an
interesting regime near the metal insulator transition driven by the charge
transfer mechanism. Relationship with cuprates and the organic superconductors
are discussed.
