I try to reproduce the dielectric function as the picture bellow using Yambo code but the values that I have found in y-axis are so much bigger [-1000,1500] compared to literature. I generated the scf file using Quantum ESPRESSO then I used Yambo to generate the dielectric function.

I have doubts that the problem can be related to the occupations type and degauss value. Actually I used occupations ='fixed' in the scf , then when I changed it to smearing the y-axis values reduced a little bit but I'm still far from the literature.

Can someone clarify my doubts about that, please? And which occupations type and degauss value I should use?

PS: I already encountered same problem in other calculations like DOS.

enter image description here

Link of the paper from which I took the picture: https://www.sciencedirect.com/science/article/pii/S092145260600189X

  • $\begingroup$ Could you please link or state the name of the literature that you mentioned where the picture is taken from? $\endgroup$ Apr 11, 2023 at 21:28
  • $\begingroup$ @AbdulMuhaymin I added the link to the post $\endgroup$
    – Camilla
    Apr 12, 2023 at 12:09
  • $\begingroup$ @AbdulMuhaymin I tried epsilon too and the values are always so high. Do you have any idea why is that? Or do you know the unit used by epsilon? $\endgroup$
    – Camilla
    Apr 12, 2023 at 15:02
  • $\begingroup$ Did you get comparable result after rescaling the values as suggested in the answer? $\endgroup$ Apr 13, 2023 at 21:53
  • 1
    $\begingroup$ I am following this book. See chapter 3 section 4: Optical Properties. The source code can be found here $\endgroup$ Apr 14, 2023 at 16:12

1 Answer 1


The plot in the reference paper is in the Arbitrary unit. So, the absolute value doesn't matter. The value can be 1 in the paper and 1000 in your calculation - it is not a problem. I think the only thing to make sure is that the overall shape is correct.

You can try choosing a suitable reference point in the paper, let's say $3 \mathrm{eV}$. Then reduce your calculated $\varepsilon_1$ value (let's say $6000$) at that point so that it matches the value given in the paper (looks like around $6$). Note the reduction factor (in this hypothetical example, it is $1000$). Then apply the same reduction factor for all of your data (i.e. divide everything by $1000$). Similarly, reduce your $\varepsilon_2$ data too. Then if you plot these reduced data, you can compare your result with the reference data.

  • $\begingroup$ I was thinking about the same thing but I needed someone to confirm to me if that's the right thing to do, thank you $\endgroup$
    – Camilla
    Apr 14, 2023 at 9:36

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