The band structure, orbital contributions to the spectral weight of the states at the top of the valence band, and the type of band gap in a CuO monolayer are investigated for different values of the hopping integrals and the Coulomb interactions on copper, \(U'_d\) , and oxygen, \(U'_p\) . The electronic structure of quasiparticle excitations is calculated using an eight-band p–d model that includes all Cu 3d and O 2p orbitals, together with the generalized tight-binding method and the the equations of motion method for Green’s functions of Hubbard operators within the multiband Hubbard model. The energy spectrum of local states and dispersionless quasiparticle excitations is obtained. The ratio \({{U'_d}}/ {{U'_p}}\) determines both the magnitude and the type of the band gap. Depending on this ratio, Mott–Hubbard (MH), charge-transfer (CT), or interorbital band gap can arise. When \(U'_d\) dominates over \(U'_p\) , the system is insulating, with a band gap opening between d-orbitals. A metallic state can be realized only when \(U'_p\) exceeds \(U'_d\) . The metal–insulator transition driven by increasing hopping integrals is possible only for \(U'_d < 1.5U'_p\) .
