We first consider self-consistent Schrödinger-Poisson calculations for nonpolar core-shell NWs with hexagonal cross-sections. As shown in Fig. , the spontaneous polarization contribution vanishes because the polarization axis is in the axial direction. The piezoelectric polarization also drops out-the strain components ε xz and ε yz are both zero since the displacements are uniform in the axial direction. It follows that all interfaces in the hexagonal NW are nonpolar, indicating that electron gas formation in these systems results exclusively from the conduction band edge discontinuity in V CB ( x, ỹ) and variations in the electrostatic potential, V( x, ỹ). Previous work by us and others have shown that electron gas formation is insensitive to local exchange-correlation effects in V xc ( x, ỹ) .