Absorption Spectrum


I see in Bethe-Salpeter equations, we are able to plot the imaginary dielectric constant against the photonic energy of light to plot the optical spectra. Is it possible to plot the absorption coefficient against the photonic energy?

The BSE part of ABINIT outputs a file named xxx_EXC_MDF that contains both the real part and the imaginary part of the macroscopic dielectric function (MDF).
All the optical constants (reflectivity, absorption, etc.) can be obtained from the MDF.
Table 11.1 of Grosso-Pastore Paravicini’s Solid State Physics give you all the desired relations.