> For the complete documentation index, see [llms.txt](https://docs.materialsproject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.materialsproject.org/methodology/materials-methodology/optical-absorption-spectra.md).

# Optical absorption spectra

The optical absorption spectra is obtained by calculating the frequency-dependent dielectric tensors using VASP. It uses independent particle approximation and assumes only vertical interband transitions to obtain the imaginary part of the dielectric tensors. Via the Kramers-Kronig relations the relationship between the dispersions of the real and imaginary parts of the dielectric function can be established. With both the real and imaginary part of the frequency-dependent dielectric tensors, one can calculate the optical absorption coefficient at different photon energies. Our results are validated against the experimental database: <https://refractiveindex.info>

For more information, please see <https://arxiv.org/abs/2209.02918>.