There are two types of interactions which determine the degree to which bands are inverted in a material: relativistic spin-orbit interactions and atomic orbital interactions. Spin-orbit coupling (SOC) effects are often regarded as the principal mechanism driving band inversion and is typically illustrated as in Figure . For example, electronic structure calculations of Bi2Se3 have shown that bands are only inverted in the presence of SOC, and exaggerated SOC strengths lead to sufficiently inverted, warped bands. Yet, the bands in rock-salt SnSe (Figure ) are more inverted than in SnTe and PbTe (Figures and), despite the stronger SOC in the tellurides due to the heavier Te atom. This is because the cation-s/anion-p interaction at the L-point is stronger in rock-salt SnSe, leading to a larger separation of the Γ + 4 band from the Γ - 4 band at the L-point (Figure ). The dissimilar band inversion mechanisms in the rock-salt family (driven by atomic orbital interactions) and the tetradymite family (driven by SOC) can also be captured by evaluating how the band inversion changes with lattice constant in the respective systems. In SnTe (Figure ) and Bi2Te3 (Figure ), the band inversion intensifies (i.e. M0 becomes more negative) as the lattice constant decreases. This is because the shorter cation-anion bond lengths lead to stronger s-p interactions in SnTe and p-p interactions in Bi2Te3, leading to a larger separation between the Γ + 4 and Γ - 4 bands at the L-point in SnTe (Figure ) and Γ-point in Bi2Te3 (Figure ). The extrapolated M0 of SnTe at the lattice constant of rock-salt SnSe is similar to the true M0 of SnSe (Figure ); however, the M0 of Bi2Se3 deviates significantly from the trend set by Bi2Te3 (Figure ). This indicates that while atomic orbital interactions are the dominant band inversion mechanism within the family of rock-salt materials, an additional effect other than atomic orbital interactions (i.e. SOC 7 ) likely affects the band inversion in tetradymite systems.