Re: [Pw_forum] phonon calculation not converge

Ari P Seitsonen Thu, 29 Oct 2015 15:35:28 -0700


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, theamount of band dispersion it etc. So indeed, if the electronic structureis not yet converged well with only Gamma point, it is better to applymore 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 theHGH/GTH pseudo potentials that you have used: We used 125 Ry for theoxygen - I would guess that the one for iron, maybe also lithium - andthat was in molecular dynamics; for phonons I would expect even higher avalue necessary.


    Greetings,

       apsi

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  Ari Paavo Seitsonen / [email protected] / http://www.iki.fi/~apsi/
  Ecole Normale Supérieure (ENS), Département de Chimie, Paris
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在 2015-10-30 00:26:09，"Xiaolin Xu" <[email protected]> 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 <[email protected]> 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 <[email protected]> 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" <[email protected]> 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

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