# Why my values of dielectric function don't match litterature (For Yambo with Quantum ESPRESSO)?

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.

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

• Could you please link or state the name of the literature that you mentioned where the picture is taken from? Apr 11 at 21:28
• @AbdulMuhaymin I added the link to the post Apr 12 at 12:09
• @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? Apr 12 at 15:02
• Did you get comparable result after rescaling the values as suggested in the answer? Apr 13 at 21:53
• I am following this book. See chapter 3 section 4: Optical Properties. The source code can be found here Apr 14 at 16:12

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.