DFPT  [SOLVED]

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DFPT  [SOLVED]

Postby wlsong » Mon Apr 01, 2019 4:35 am

Which parameter is added to the LO-TO split when calculating the phonon spectrum? :)
wlsong
 
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Re: DFPT

Postby mverstra » Mon Apr 01, 2019 1:46 pm

See, e.g. eq 61 in

http://iffwww.iff.kfa-juelich.de/~wortm ... l45/C2.pdf

There is a sum evaluated over the different born charges projected on the TO mode you want to renormalize. The change is non-analytical in the sense that it depends on which direction your q vector points when you take the limit q -> 0 (discontinuous at Gamma).
Matthieu Verstraete
University of Liege, Belgium
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Re: DFPT

Postby wlsong » Mon Apr 01, 2019 3:39 pm

Hello. Thank you very much for your reply. I really count the ion system. I am repeating the literature to calculate the phonon spectrum of barium titanate. There is a split in the literature, I think it should be a parameter to split
wlsong
 
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Re: DFPT

Postby mverstra » Mon Apr 01, 2019 3:52 pm

I don't understand what you mean by parameter.

The formula cited calculates the value of the LO-TO phonon frequency split, and is calculated in anaddb for each q vector direction (q->0) given in the "second list of q2ph" (see the tutorials on response functions).
Matthieu Verstraete
University of Liege, Belgium
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Re: DFPT

Postby wlsong » Wed Apr 03, 2019 10:38 am

Thank you very much, I have solved my problem. :P :P
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