### DFPT [SOLVED]

Posted:

**Mon Apr 01, 2019 4:35 am**Which parameter is added to the LO-TO split when calculating the phonon spectrum？

The meeting place for ABINIT users and developers

https://forum.abinit.org/

Page **1** of **1**

Posted: **Mon Apr 01, 2019 4:35 am**

Which parameter is added to the LO-TO split when calculating the phonon spectrum？

Posted: **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).

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).

Posted: **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

Posted: **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).

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).

Posted: **Wed Apr 03, 2019 10:38 am**

Thank you very much, I have solved my problem.