[Wien] regarding k-mesh and tolf

[chin Sabsu]

Dear Xavier Sir,
Sorry, I understood my mistake in my phonon bands. I must go for higher supercell distorted structures and the present bands are not the accurate one. However, the rest queries are still looking for the answer.
PBE0 is good for optimization?From your experience how much time it will take for optimization? Due to limited facilities, your answer will help me a lot.
One alternative for me is (as adviced by you in a thread in quite past), I will optimize the structure from Wien2k and the phonon calculations will be carried out on QE.
Thank you very much for the excellent and productive reply.
Chin S.

 

    On Sunday 28 January 2018, 3:31:32 PM IST, chin Sabsu <chinsabsu at yahoo.in> wrote:  
 
  Thanks Sir for your valuable time for me.I will try to use PBE0. I am using PBE0  first time and do not know how much time wien2k will take for it. I will update here if I get an update.
Anyway, I have calculated phonon bands using PBESol for my two systems (one showing zero bandgaps and another showing some band gap) with 1x1x1 supercell. The list is not allowing to send docs me so the same I am sending you in your private email (anyone else interested can ask me for the bands). The phonon band ( case_1.pdf , the one which giving zero band gap) is showing that structure is thermodynamically not stable while another case (case_2.pdf; the one which is showing some band gap) is thermodynamically stable. Anyway, more comments can be made after having accurate/PBE0 calculations. I am also sending you FORCE_SETS file.
Again thanks a lot for your kind help.
Regards
Chin S.

 
 
    On Sunday 28 January 2018, 2:52:34 PM IST, Xavier Rocquefelte <xavier.rocquefelte at univ-rennes1.fr> wrote:  
 
  
Here is a link towards a paper which treats such systems using GGA and HSE06. Indeed, with GGA the band gap is nearly zero for some of them. 
 
 
https://arxiv.org/pdf/1706.08674.pdf
 
The point is that it seems to me that it will not be too much problematic although your band gap is zero if the bands are simply touching at the Fermi level. 
 
 
You must check your band structure first. 
 
 
In the paper they show HSEO6 band structures which clearly confirm that GGA+U or onsite-hybrid will not be useful. 
 
 
One option for you could be to do band structure using GGA and Full-hybrid (HSE06 or PBE0) to compare and discuss the differences. Then if the difference is only band gap reduction, you could use GGA for the phonons calculations. In addition, it will allow you to estimate the residual forces using both GGA and hybrid, which will be one more confirmation (or not) that GGA is sufficient for your system. 
 
 
Cheers
 
Xavier
 
 
 Le 27/01/2018 à 16:01, chin Sabsu a écrit :
  
Sir, it is A2BX6,  x is halogen.
 
 Sent from Yahoo Mail on Android 
 
  On Sat, Jan 27, 2018 at 7:23 PM, Xavier Rocquefelte <xavier.rocquefelte at univ-rennes1.fr> wrote:   _______________________________________________
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