The six 3m-symmetric carrier pockets which are offset from the L-plane in rock-salt SnSe and SnS (Figures ) indicate that out-of-plane interactions are necessary to properly model the electronic structures of these compounds. As shown in Figure , the k • p model can capture the general electronic structure features of all rock-salt IV-VI compounds when in-plane and out-ofplane interactions are included. A single carrier pocket is possible regardless of whether the bands are normal (Figure ) or in- verted (Figure ). The electronic structures of PbTe, PbSe, PbS, and GeTe can therefore be represented by Figure , whereas the electronic structure of the single-valleyed SnTe with inverted bands can be represented by Figure . We obtain a ring-like Fermi surface (Figure ) when Equation ( ) is satisfied. The ring-like conduction bands of GeSe and GeS (Figures and) can be modeled by Figure . The ring-like Fermi surface can be split into six carrier pockets by including the R 1 parameter (Figure ), which can be further broken into three carrier pockets on each side of the L-plane by the R 2 parameter (Figure ). As a result, the R 1 and R 2 parameters enforce the three-fold rotational symmetry of the carrier pockets, similar to the hexagonal warping term used to model the surface states of Bi 2 Te 3 . It is interesting that rock-salt IV-VI compounds with inverted bands show no more than six carrier pockets, even though the 3m symmetry of the L-point can permit up to twelve pockets. This can be understood by identifying the mirror planes of the L-point (Figure ); if the pockets are offset from the mirror planes, then there must be twelve pockets surrounding each L-point (Figure ), as opposed to six when the pockets lie on the mirror planes (Figure ). We speculate that the chemical interactions which force the pockets to lie on the mirror planes are the same interactions as those which create the pockets at L in rock-salt IV-VI compounds. As described in Refs. 13 and 34, interactions between cation-p and anion-p states leads to both the valence and conduction band extrema at the L-point (k x = k y = k z = ±π/a). These same interactions also affect the band energy when only two of k x , k y , or k z is ±π/a, as evidenced by the second valence band maximum appearing along the Σ-line near (±π/a, ±π/a, 0). The L and Σ pockets merge to form a tube-like Fermi surface approximately in the shape of a cube with corners (±π/a, ±π/a, ±π/a), as inscribed in the Brillouin zone in Figure . When band inver-sion forces the band extremum off L, the extremum then moves down the cube edge which lies on a mirror plane leading to six carrier pockets for each L point.