and is non-degenerate. The second band behaves in a similar fashion. The third band appears to maintain a minimum away from the $\Gamma$-point in the $\Sigma_{\rm{TET}}$-direction (which is equivalent to the $\Delta_{\rm{FCC}}$-direction; see App. \[sec:bravais\]), but in a less-parabolic fashion than the lower two; its minimum is similar to the value at $\Gamma$. This band is non-degenerate along this particular direction in $k$-space, but due to the supercell symmetry it is actually 4-fold degenerate, in contrast to the other bands. The Fermi level for the doped system is also shown, clearly being crossed by all three of these bands which are therefore able to act as open channels for conduction.

![Bandstructure of the 40-layer tetragonal system, zoomed in on the $\Delta$ band, calculated with (a) PW (<span style="font-variant:small-caps;">vasp</span>), (b) DZP (<span style="font-variant:small-caps;">siesta</span>), and (c) SZP basis sets.[]{data-label="fig:zoom"}](d1zoom){width="\linewidth"}

As mentioned above, the bandstructures are similar across all methods, but upon detailed inspection important differences come to light. A closer look at the $\Delta$ band shows a qualitative difference between the predictions using SZP (Fig. \[fig:zoom\]c) and the PW and DZP results (Figs. \[fig:zoom\]a & \[fig:zoom\]b): the models with a more complete basis predict the band minimum to occur in the $\Sigma_{\rm{TET}}$ 