dense mesh becomes extremely time consuming we present in the next section conductivity spectra calculated on the 80$\times$80$\times$48 mesh. It is worth noting, that above 0.5 eV convergence of the calculated conductivity spectrum is achieved already on the 32$\times$32$\times$16 mesh.

Analysis and Results
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![(a) Real and (b) imaginary part of conductivity. Solid and dashed lines represent the measured and extrapolated frequency regimes respectively. The markers at 8 cm$^{-1}$ in (a) represents the dc conductivity calculated from \[fig:ref\](c)[]{data-label="fig:sigma"}](sigma2.png "fig:"){width="48.00000%"}

The complex optical conductivity of the sample has been calculated from the reflectivity spectrum using KK constrained VDF fitting [@kuzmenko2005kramers]. This technique is an alternative to using conventional KK transformations to calculate the complex conductivity from a single measurement and is particularly useful in dealing with multiple reflection/transmission data from different disjoint frequency ranges. The method, implemented using the software RefFIT, involves an initial fitting of the reflectivity spectra to a standard Drude-Lorentz oscillator model with a few oscillators and then performing a KK constrained variational fitting with many oscillators of the difference spectra. For YbMnBi$_2$, the reflectivity spectra for each temperature has been fitted with one Drude and six Lorentz oscillators which has then been subjected to the VDF 