Dear DFT Community, 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. Therefore i am attaching few files with expected results, calculated results and vasprun.xml and OUTCAR in case you want to see your self.
Dear Muhammad Usman Javed , I'm not used to the VASP, but the results you reported are 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. Reading the "OUTCAR", it seems that VASP is using independent particle approximation, but I didn't find any information of the transfered momentum. To reproduce the experimental results the tranfered momentum should be set to zero (or almost zero, due to numerical limitations).
Please see Article TurboEELS - A code for the simulation of the electron energy...
.Saeed S. I. Almishal told in a previous answer to use BSE approximation, but it is appliable to semiconductors not for metals.
Interestingly i found these papers which discusses about few models for fitting of calculated and measured 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.
https://doi.org/10.1117/1.JNP.8.083097
https://doi.org/10.1364/OME.388060
Use the following python code to extract real and imaginary parts:
import pymatgen.io.vasp as vasp
import numpy as np
import matplotlib
matplotlib.use('agg')
from matplotlib import pyplot as plt
import pymatgen as mg
vr = vasp.Vasprun('vasprun.xml')
energies = vr.dielectric[0]
e1 = np.array(vr.dielectric[1])
e1x = e11[:,0]
e1y = e11[:,1]
e1z = e11[:,2]
e2 = np.array(vr.dielectric[2])
e2x = e12[:,0]
e2y = e12[:,1]
e2z = e12[:,2]
etot = (e1x+e1y+e1z)/3
etoti = (e2x+e2y+e2z)/3
plt.figure()
plt.title("Complex Dielectric Function")
plt.xlabel("Energy")
plt.ylabel("Dielectric function")
plt.plot(energies, etot, 'r', label = "Real")
plt.plot(energies, etoti, 'b', label = "Img")
plt.legend()
plt.grid('on')
plt.xlim(0,20)
plt.minorticks_on()
plt.savefig("Dielectric.pdf")
Bishal Babu Dumre Thanks for writing these code line to extract imaginary and real parts of permittivity from vasprun.xml , however after multiple time running and confirmation i am sorry to say i wasn't able to extract anything using this code. i am attaching the output file after running python code kindly take a look and guide further. your assistance will be appreciated also i humbly ask to take a look on above mentioned data fitting model(paper) and try to generate few line of code using python.
There was a small error in the code that I provided you before. The attached file is what I got from your vasprun.xml. Please use the following debugged code in your computer. This new code will work:
import pymatgen.io.vasp as vasp
import numpy as np
import matplotlib
matplotlib.use('agg')
from matplotlib import pyplot as plt
import pymatgen as mg
vr = vasp.Vasprun('vasprun.xml')
energies = vr.dielectric[0]
e1 = np.array(vr.dielectric[1])
e1x = e1[:,0]
e1y = e1[:,1]
e1z = e1[:,2]
e2 = np.array(vr.dielectric[2])
e2x = e2[:,0]
e2y = e2[:,1]
e2z = e2[:,2]
etot = (e1x+e1y+e1z)/3
etoti = (e2x+e2y+e2z)/3
plt.figure()
plt.title("Complex Dielectric Function")
plt.xlabel("Energy")
plt.ylabel("Dielectric function")
plt.plot(energies, etot, 'r', label = "Real")
plt.plot(energies, etoti, 'b', label = "Img")
plt.legend()
plt.grid('on')
plt.xlim(0,20)
plt.minorticks_on()
plt.savefig("Dielectric.pdf")
Dear Bishal Babu Dumre thanks for helping me to plot the dielectric constants using python, but that's not the solution of problem. If you follow the thread in first question i already attached my calculated Dielectric constant with no difference to yours. Also if you see the attached literature review it shows that these lines are from inter-band rather than intra band or total. could you help us to work on data fitting to get the Drude model right using these calculated files.
Hello Muhammad Usman Javed , can you told me from which article or book did you get the real and imaginary part of epsilon (Litterature imaginary and real)?
Thank you.
Dear Zahira Faiza Meghoufel attach is the article. These DFT calculation of Au that exhibits the complex dielectric permittivity are dependent upon two contribution i.e. e(w) = e(w) intra + e(w) inter band. The latter part has been calculated by Lorentz contribution and the former is Drude model. Wien2K , Vasp and other calculation use Kramer kronig transformation for Real and imaginary part of these complex permittivity. However in future the DFT calculation user will find that the interband contribution is calculated and intra-band i.e Drude model is missing from their calculations, which i will soon update once i complete my verification.
Muhammad Usman Javed thank you very much dear researcher.i will check it.
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