[Pw_forum] Phonon Dispersion with LO-TO splitting

[Eyvaz Isaev]

Dear Srijan,


>  Thanks a lot for your helpful reply. 
You are welcome.

>However, in practice, sometime smearing keyword needs to be used for a 
>complicated
>semiconductor or insulator in order get a faster scf convergence. And hence, 
>it is better to identify a system is non-metal or metal by its band-gap instead 
>of smearing 
>
>keyword. 

As you were interested in LO-TO splitting, in fact, I meant the Gamma point 
calculation only.

>In particular, phonon code in QE complain a lot if the system is a 
>spin-polarized  insulator. 
>
>For example,    "fixed occupations and lsda need tot_magnetization",  
>"The phonon code with constrained magnetization is not yet available", 

Yes, agree. Such kind systems still seem to  be  problematic.  At least, to me.

> " IF (epsil.AND.lgauss) &  CALL errore ('phq_readin', 'no elec. field with 
>metals', 1)", etc. etc.

But this one is correct from the physical basics. See any good textbook on solid 
state physics, or review by 

S.Baroni, , S. de Girocoli,  A. Dal Corso and P. Giannozzi, Rev.Mod.Phys., 73,  
515, 2001.

>At least for the last error, I guess, it is better if we write, 
> " IF (epsil.AND.gap_zero)  &  CALL errore ('phq_readin', 'no elec. field with 
>metals', 1)"
> in place of the current existing statement. Then it will give a chance to 
>compute \epsil also for 
>
> an insulating system which uses "smearing" keyword just for faster 
convergence.

I am not sure, this will fix the convergence problem. Besides, see the 
above-mentioned comment.  This prevents 

an attempt to calculate Z* and \epsilon for metallic systems and is correct.

>For magnetic insulator, is there any further example which shows a 
>phonon-dispersion with LO-TO splitting ? 
>

In fact, I do not remember any such kind  example. 

Bests,
Eyvaz,
______________________________________
Departmenmt  of Physics, Chemistry and Biology,
Linkoping University, Sweden
eyvaz_isaev at yahoo.com, isaev at ifm.liu.se


      
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