[Pw_forum] Weird jump in phonon dispersion at Gamma point

[Lorenzo Paulatto]

On 9 November 2012 01:14, Yao Yao <yao.yao at unsw.edu.au> wrote:

> Looks this is similar to the problem reported here
> http://www.democritos.it/pipermail/pw_forum/2009-June/013250.html
> But seems that problem has been solved according to the following email. Is
> this another problem in q2r or matdyn?
>
>
As I stated several times in the discussion that you are linking, those
"weird jumps" are *an actual physical phenomenon*. If you remove them *you
are doing it wrong*! The problem is not with the code, but your
understanding of the problem. I do not want to be rude, this is just to *
warn* you that you may be going in the wrong direction.

Anyway:
* if you have understood that LO-TO splitting is induced by the long range
interaction of effective charges in polar insulators/semiconductors
* if you still think that removing this splitting is the right thing to do
* if you promise to *not* cite me as the source of this information

then, edit PH/matdyn.f90 and around line 466 replace
           ELSE
              lo_to_split=.TRUE.
           ENDIF
           !
           CALL nonanal (nat, nat_blk, itau_blk, epsil, qhat, zeu, omega,
dyn)
with
           ELSE
              lo_to_split=.FALSE.
           ENDIF
           !
           !!! CALL nonanal (nat, nat_blk, itau_blk, epsil, qhat, zeu,
omega, dyn)
i.e. set lo_to_split to .false. in every case and do not compute the
non-analitical long-range term.

Then recompile the phonon code

best regards


-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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