The valence band maximum is a singly-degenerate, relatively light band which emerges from the flatter valence bands at the Γ point (Figure ). The charge density of this band exhibits p z -type orbitals centered on the Sb atoms of the (M Sb 4 ) m-tetrahedra and nonbonding Sb atoms (Figure ) with less contribution from the trimer. The fact that only the p z orbitals of Sb atoms make up the light valence band suggests that hole transport should be somewhat anisotropic with different electrical conductivity in the x and y directions.