We have investigated the electronic and structural properties of CFO and CBO, using DFT on the PBE+U level. According to the DOS and compared to experiments, the PBE+U is the better approach to describe the semiconducting behavior of CBO and CFO compared to PBE. The DOS of the surfaces indicates midgap states for cation-deficient surface terminations in both materials. This could enable higher absorption efficiency for Cu-deficient surfaces. The midgap states, generated by atoms in the outermost layer, can be confirmed by the Bader charge analysis. With the help of the Bader charges we could see fast convergence of charges within the outermost layer of the stoichiometrically terminated surfaces of CFO and CBO. Additionally, charge fluctuations for Fe-or Bi-deficient surface terminations can lead to unstable surfaces.