[Pw_forum] phonon calculation not converge

[Ari P Seitsonen]

Dear Xiaolin, Jiqiang et co,

   Did you re-run 'pw.x' using the 'K_POINTS automatic // 1 1 1  0 0 0' 
before trying to run 'ph.x'?

   On the other hand the number of k points depends on your system, the 
amount of band dispersion it etc. So indeed, if the electronic structure 
is not yet converged well with only Gamma point, it is better to apply 
more k points. This you can do by testing for the convergence.

   By the way, the cut-off energy of 80 Ry is probably far too low for the 
HGH/GTH pseudo potentials that you have used: We used 125 Ry for the 
oxygen - I would guess that the one for iron, maybe also lithium - and 
that was in molecular dynamics; for phonons I would expect even higher a 
value necessary.

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Ecole Normale Supérieure (ENS), Département de Chimie, Paris
   Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


>
> 在 2015-10-30 00:26:09，"Xiaolin Xu" <xiaolin0314 at gmail.com> 写道：
>
>> Hi Jiqiang,
>>
>>
>> Thank you very much for your help! 
>>
>> I tried using only gamma point, but I got an error message when I calculated phonon saying "can't start from gamma tricks...". Besides, I need to calculate the raman frequencies after phonon calculation, so I think it's better if I use more k points.
>>
>> Have you tried Raman calculation? Could you give me more advice?
>>
>> Best,
>>
>> Xiaolin
>>
>>
>> On Wed, Oct 28, 2015 at 10:21 PM, Xiaolin Xu <xxu2 at caltech.edu> wrote:
>>
>> Hi Jiqiang,
>>
>> Thank you very much for your help! 
>>
>> I tried using only gamma point, but I got an error message when I calculated phonon saying "can't start from gamma tricks...". Besides, I need to calculate the raman frequencies after phonon calculation, so I think it's better if I use more k points.
>>
>> Have you tried Raman calculation? Could you give me more advice?
>>
>> Best,
>>
>> Xiaolin
>>
>>
>> On Wed, Oct 28, 2015 at 6:20 PM, jqli14 <jqli14 at fudan.edu.cn> wrote:
>> (1)employ k_points gamma instead of k_pionts automatic 1 1 1 0 0 0, although both give the same result, but the later does not call the gamma point specific algorithm to speed the calculation.
>> (2)if it can not converge within handreds of electronic steps, reduce the value of mixing_beta or change the mixing_mode.
>>
>> Jiqiang Li
>>
>>
>> 在 2015-10-29 07:57:58，"Xiaolin Xu" <xiaolin0314 at gmail.com> 写道：
>>
>>> Dear all,
>>>
>>> I was doing phonon dispersion calculations for lithium iron phosphate. However, the calculation speed is really slow and it does not converge. Is this because my system is too big? There are 28 atoms in the unit cell. My input file is like this:
>>> (1)
>>>
>>>
>>> &CONTROL
>>> calculation = "scf",
>>> pseudo_dir = "/home/xiaolin/pseudo",
>>> outdir = "/home/xiaolin/test2",
>>> tstress=.true.,
>>> tprnfor=.true.,
>>> nstep=100,
>>> /
>>>
>>> &SYSTEM
>>> ibrav = 8,
>>> celldm(1) = 19.749526
>>> celldm(2) = 0.582432,
>>> celldm(3) = 0.454693,
>>> nat = 28,
>>> ntyp = 4,
>>> ecutwfc = 80.D0,
>>> /
>>>
>>> &ELECTRONS
>>> mixing_beta = 0.7,
>>> /
>>>
>>> &IONS
>>> /
>>>
>>> ATOMIC_SPECIES
>>>
>>> Li 6.941 Li.pbe-s-hgh.UPF
>>> Fe 55.845 Fe.pbe-sp-hgh.UPF
>>> P 30.97376 P.pbe-hgh.UPF
>>> O 15.9994 O.pbe-hgh.UPF
>>> ATOMIC_POSITIONS (alat)
>>> Li 0 0 0
>>> ...
>>> K_POINTS (automatic)
>>> 1 1 1 0 0 0
>>>
>>> (2)
>>>
>>> Normal modes for lifepo4
>>> &inputph
>>> tr2_ph=1.5d-5,
>>> amass(1)=6.941,
>>> amass(2)=55.845,
>>> amass(3)=30.97376,
>>> amass(4)=15.9994,
>>> outdir = '/home/xiaolin/test2',
>>> trans=.true.,
>>> asr=.true.,
>>> nogg=.true.,
>>> fildyn='dmat.lifepo4'
>>> /
>>> 0.0 0.0 0.0
>>>
>>>
>>>
>>> Thank you in advance!
>>>
>>>
>>> Lin
>>
>>
>>
>