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Problem in optical properties
Posted: Thu Sep 08, 2022 5:12 am
by abdul_jaleel1
Dear Users
I want to calculate Frequency dependent dielectric tensor with and without local field effects in RPA of CuO monoclinic phase. Job completed without errors and warning but unable to get dielectric tensor. All data attached.
Re: Problem in optical properties
Posted: Thu Sep 08, 2022 7:12 am
by merzuk.kaltak
Dear Abdul,
could you please upload your data in a "zip" format?
I have trouble extracting it with "unrar".
Thanks in advance
Re: Problem in optical properties
Posted: Fri Sep 09, 2022 6:27 am
by abdul_jaleel1
attached please.
Re: Problem in optical properties
Posted: Fri Sep 09, 2022 12:04 pm
by merzuk.kaltak
Dear Abdul,
the dielectric tensor is given in the vasprun.xml file as described in our
tutorial on dielectric properties of SiC.
Looking into vasprun.xml you will typically find three sets of data. Please take a look at the tutorial, which also contains a bash script that extracts the data from the file.
For convenience, the very same script is given below:
Code: Select all
awk 'BEGIN{i=1} /imag/,\
/\/imag/ \
{a[i]=$2 ; b[i]=$3 ; i=i+1} \
END{for (j=12;j<i-3;j++) print a[j],b[j]}' vasprun.xml > imag.dat
awk 'BEGIN{i=1} /real/,\
/\/real/ \
{a[i]=$2 ; b[i]=$3 ; i=i+1} \
END{for (j=12;j<i-3;j++) print a[j],b[j]}' vasprun.xml > real.dat
# you can use the following line inside the gnuplot terminal to plot the data
# plot [0:25] "imag.dat" using (\$1):(\$2) w lp, "real.dat" using (\$1):(\$2) w lp
This script will scrap the file vasprun.xml for lines that start with
and will dump the real and imaginary part into "real.dat" and "imag.dat", respectively.
More precisely, following data contains the q->0 limit of the imaginary part of the dielectric tensor
(also known as the HEAD of the microscopic dielectric tensor eps_{G=0,G'=0}(q=0, omega) ).
Code: Select all
<dielectricfunction comment="HEAD OF MICROSCOPIC DIELECTRIC TENSOR (INDEPENDENT PARTICLE)">
<imag>
<array>
<dimension dim="1">gridpoints</dimension>
<field>energy</field>
<field>xx</field>
<field>yy</field>
<field>zz</field>
<field>xy</field>
<field>yz</field>
<field>zx</field>
<set>
<r> 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
<r> 0.4627 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
<r> 0.9250 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
<r> 1.3866 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
<r> 1.8472 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
<r> 2.3065 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 </r>
... ^ ^ ^ ^ ^ ^ ^
| | | | | | |
energy eps_xx eps_yy esp_zz esp_xy eps_yz eps_xz |
Here the first column of numbers at the bottom are the frequency (energy), followed by the diagonal components xx,yy,zz and the off-diagonal ones xy,yz,zx.
Please note, you might want to increase
NBANDS to include more unoccuppied states in your calculation to obtain more reliable results.
Re: Problem in optical properties
Posted: Tue Sep 27, 2022 1:24 pm
by abdul_jaleel1
I have used the same script to grep real.dat and imag.dat files but unfortunately I have not found the required results. please have a look to attached files.
Re: Problem in optical properties
Posted: Sun Oct 30, 2022 2:12 am
by SKM
Dear Admin,
as per the reply below, i am referring to the following;
the first column of numbers at the bottom are the frequency (energy), followed by the diagonal components xx,yy,zz and the off-diagonal ones xy,yz,zx.
Now,I understand that these
imaginarydata correspond to the
optical absorption spectrum. (hope the understanding is right)
What these
xx and
yy diagonal components really mean in terms of optical absorption? In other words, if i plot Energy Vs xx or yy, data, then what is the physical meaning (or significance) of these data/plots?
Regards
Re: Problem in optical properties
Posted: Wed Nov 02, 2022 10:12 am
by merzuk.kaltak
Dear SKM,
unfortunately we do not have the capacity to answer physics questions.
In short, the individual components of the dielectric tensor can be connected to the absorption and reflection of light from and into a specific direction of the system.
A good explanation of the dielectric tensor can be found in textbooks or even
here.
Re: Problem in optical properties
Posted: Fri Nov 04, 2022 2:38 am
by SKM
Dear Merzuk
thank you for the reply.
i could see some reference papers about these results of tensor direction of absorption.
However, for obtaining the 'dielectric properties in VASP we must expose the crystal with electric field'. Right?
Now the fundamental query i got is 'In which direction of the crystal the incident Electric field is assumed by VASP?"
Regards
skm
Re: Problem in optical properties
Posted: Fri Nov 04, 2022 9:03 am
by merzuk.kaltak
Dear SKM,
To answer you question:
An external electric field is not necessary to determine the dielectric matrix. The same matrix can be determined with density functional perturbation theory (which uses the gradient of the cell-periodic wavefunction). This method is selected in vasp with
LEPSILON and solves the Sternheimer equation for a perturbation to arrive at the complete 3x3 dielectric matrix (including other quantities like the Born effective charges).
In contrast, the
LCALCEPS method uses three external electric fields to determine the very same dielectric matrix.
By default, the code computes the response of the crystal to an electric field in x, the response of a field in y and finally in z direction to gather the complete 3x3 dielectric response matrix. However, you may also calculate the response of the crystal to one specific electric field with
EFIELD_PEAD. This will give you only three components of the dielectric matrix corresponding to the applied field.
Please consider
the lecture notes on dielectric properties found on our
wiki page.
Re: Problem in optical properties
Posted: Sun Mar 19, 2023 2:50 am
by SKM
Thank you
Regards