to inter-band electronic transitions. To investigate this further, the Drude contribution (which mostly captures the intra-band optical conductivity) was subtracted. In general, strong electronic correlation can give low frequency intra-band contributions that would not generally be captured through a Drude term only. One possible way to isolate such effects is through the extended Drude model [@allen1977optical] analysis which can account for inelastic scattering due to electron-electron or electron-phonon interactions that can be frequency dependent even at low frequencies. However, the extended Drude model is only reliable much below the energy scales of inter-band transitions and thus it is not particularly useful in this context where the lowest possible inter-band transition could be as low as 200 cm$^{-1}$. We will therefore ignore such effects for now and assume that all the remaining high frequency optical conductivity is primarily from inter-band transitions and compare it to the inter-band optical conductivity calculated from band structure.

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![(a) Band structure calculated along symmetry lines in tetragonal BZ. Bands crossing the Fermi level, which are discussed below, are plotted with blue (37,38), red (39,40), and green (41,42) lines. and (b) comparison of the calculated optical conductivity with experiment[]{data-label="fig:bs"}](S1_band.png "fig:"){width="48.00000%"}

Calculated inter-band optical conductivity (see figure 