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I am trying to determine the optical properties of bulk Aluminium and related alloys using Quantum ESPRESSO. I am using both the epsilon.x and the simple.x modules to get wavelength-dependent dielectric functions. However, when comparing to experimental data, the results are not in good agreement, even trying to adjust the inter and intra-smearing parameters. I simulated and compared the results for Gold and Silver alloys with no major problems (results agreed very well with the experimental ones), but with the Aluminium, I faced lots of difficulties. In the literature I found

From a convergence study on the dielectric function, we decided to employ an interpolation k-grid of 64x64x64 and η = γ = 0,1 eV in SIMPLE for each elemental metal considered, with the exception of elemental aluminum for which, because of very slow convergence of ε_inter with respect to k-point sampling...

Are there any other options beyond increasing the k-sampling and the number of unoccupied bands, to achieve better results?

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    $\begingroup$ +1. But what is the question: "why is aluminum difficult?" or "Is there anything I can do other than icnreasing the k-sampling and number of unoccupied bands?" If you want answers to both questions I think you have to ask both questions (separately). $\endgroup$ Sep 28 '20 at 20:11
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    $\begingroup$ Hi @NikeDattani, I guess both... I gonna rephrase the question and add a new, exactly as you proposed! Thanks. $\endgroup$ Sep 29 '20 at 17:13
  • $\begingroup$ @AnibalBezerra I would suggest the BerkeleyGW package for your calculation, in which an interpolation tool is provided to obtain the optical properties with dense k-mesh. $\endgroup$
    – Jack
    Apr 14 at 0:49
  • $\begingroup$ Thanks @Jack I gonna take a look at it! $\endgroup$ Apr 14 at 17:15

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