I have calculated Frequency dependent optical permittivity of Au using (VASP) my INCAR tag includes LOPTICS=.TURE., my OUTCAR has expected frequency dependent IMAGINARY DIELECTRIC FUNCTION and so to speak the data in xx yy zz xy yz zx format. Unfortunately when it comes to plotting I have seen a very strange behavior i.e. the Au plots are for interband , rather than intraband or total. I used p4V , vaspkit , bash files to separate out the Imaginary and real files but results have been shown are same and not responding according to literature. I shall be highly thankful to highlight the problem in my calculation. Kramer-Kronig transformation is not enough using LOPTICS? on the other hand GW0+BSE and ALGO CHI takes a lot of memory and system can't finish the calculation.Added picture is desired plotting but my calculation only shows the interband optical losses

  • $\begingroup$ +1 and welcome to our community! Thank you for your contribution and we hope to see much more of you in the future!! Just please look at the edits I made because the questions here have some strict standards which you'll need to follow for future questions. $\endgroup$ Dec 31, 2020 at 8:51
  • $\begingroup$ You should show your results and give the reference of the cited figure. $\endgroup$
    – Jack
    Jan 1, 2021 at 23:52
  • $\begingroup$ Could you provide the plot of the imaginary part of the dielectric function? I don't know if I understood your question, but the e1 component shown in the figure above seems to be right. The difference between the experimental and DFT results is expected due to the approximations used to evaluate the dielectric function. If I'm not wrong it was used Independent Particle Approximation, am I right? $\endgroup$ Jan 4, 2021 at 18:22
  • $\begingroup$ researchgate.net/post/… This link includes the problem and attached files kindly follow. I am not familiar with this platform and my files are not completely uploading here on MATTER MODELING. $\endgroup$ Jan 6, 2021 at 4:02

1 Answer 1


I took a look at the files posted on the Research gate platform.

I'm not used to the VASP, but the results you reported are a bit strange. I've got the same kind of outputs using the EELS package from the Quantum ESPRESSO library, which uses the Quantum Liouville equation for the charge-density susceptibility.

The reason may be the approximation VASP uses and the parameters used to perform the calculation. Reading the "OUTCAR", it seems that VASP is using independent particle approximation, but I didn't find any information on the transferred momentum. To reproduce the experimental results, the transferred momentum should be set to zero (or almost zero, due to numerical limitations).

  • $\begingroup$ Interestingly i found these papers which discusses about few models for fitting the calculated and measured of dielectric constant for few metals. These models includes Drude-Lorentz model, PSO(particle swarm Optimization) etc. It means that KK transform has less accuracy for calculating the dielectric constants. doi.org/10.1117/1.JNP.8.083097 doi.org/10.1364/OME.388060 $\endgroup$ Jan 7, 2021 at 12:24

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