Calculation of spontaneous polarization using vasp 5.2

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Amritendu · #1 Post by **Amritendu** » Thu Aug 26, 2010 1:54 pm

Hi all,
I was trying to calculate sp. polarization of tetragonal BaTiO3 using vasp 5.2. Therefore, I switched on the LCALCPOL tag, and provided PREC = Med, EDIFF = 1E-6, ISMEAR = 0 and DIPOL = 0.25 0.25 0.25 ( according to the manual) In the OUTCAR file I obtained the following line:

CALCP: cpu time 221.71: real time 72.93

Total macroscopic dipole moment: p[mac]=( 0.00000 0.00000 2.58238 ) electrons Angst

According to the manual I should obtain two lines, one for ionic dipole moment and the other for electronic dipole moment. I am not getting that. can anyone help me sort this out ?
Secondly, the polarization value that I am getting is far from the actual value. while the experimental value is ~ 25-30 micro C/ cm^2 I am getting ~64 micro C/ cm^2 . I have used experimental lattice parameters. Can any one help me out on this ?
Thanks..
Amritendu

ynwu · #2 Post by **ynwu** » Thu Aug 26, 2010 6:23 pm

I was confused about this question weeks ago and I figure it out now. If you use LCALCPOL tag, you will get only one line (as you got), which is the electronic part of total polarization. To get the total polarization, you need to calculate ionic part by hand, which is not too hard.

Amritendu · #3 Post by **Amritendu** » Fri Aug 27, 2010 10:28 am

Thanks for your reply. Could you please explain, how to calculate the ionic part?

ynwu · #4 Post by **ynwu** » Fri Aug 27, 2010 3:42 pm

It is basically summation of (Ri-Rcenter)*qi. You can look into the code for details

Amritendu · #5 Post by **Amritendu** » Sun Aug 29, 2010 5:33 pm

Can anyone please let me know if the p[mac] term (calculated using LCALCPOL tag in vasp 5.2) is a measure of spontaneous polarization of a ferroelectric system when the corresponding paraelectric phase has zero polarization ?

happyer225 · #6 Post by **happyer225** » Tue Nov 23, 2010 12:52 am

Recenly, I encountered the same problem. And I want to know how to calculate the ionic part. Should we have to back to using the Berry Phase method to calculate the ionic part? Thank you in advance!