The conduction band minimum is determined by the relative energies of the σ * bands originating from the (X 3 ) 7-trimers and the nonbonding A orbitals, and the valence band maximum at the Γ point is determined by the energies of the p z orbitals of X atoms that are either nonbonding or involved in the (M X 4 ) m-tetrahedral units. This may explain the saturation in the measured Seebeck coefficient of Yb 14-x Pr x MnSb 11 with increasing Pr content, where the band gap remains unchanged past a certain Pr content likely due to the fixed energies of the Sb-derived band edges.