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DFPT  [SOLVED]

Posted: Mon Apr 01, 2019 4:35 am
by wlsong
Which parameter is added to the LO-TO split when calculating the phonon spectrum´╝č :)

Re: DFPT

Posted: Mon Apr 01, 2019 1:46 pm
by mverstra
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).

Re: DFPT

Posted: Mon Apr 01, 2019 3:39 pm
by wlsong
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

Re: DFPT

Posted: Mon Apr 01, 2019 3:52 pm
by mverstra
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).

Re: DFPT

Posted: Wed Apr 03, 2019 10:38 am
by wlsong
Thank you very much, I have solved my problem. :P :P