[Pw_forum] ph.x cannot reach convergence within 100 steps

Eyvaz Isaev eyvaz_isaev at yahoo.com
Thu Jul 21 10:10:10 CEST 2011 

>Then,  may I make a conclusion that this structure or composition is unstable?
 
If  you have imaginary frequency, yes. If the structure is a high temperature phase, it is another story. DFPT works at  low  temperatures (strongly speaking at T=0K).

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


________________________________
From: GAO Zhe <flux_ray12 at 163.com>
  .

I have obtained the convergent result by decreasing alpha_mix(1) from 0.7 to 0.4. But the result has imaginary frequency (about -80 cm^-1) at X(100).
Further more, I also tried VCA (by virtual.x) +DFPT method for the same composition and strucutre, X(100) still had imaginary frequency (also about -80 cm^-1).
Then,  may I make a conclusion that this structure or composition is unstable?
Looking forward to your reply.
Best Regards.

--
GAO Zhe
CMC Lab, MSE, SNU, Seoul, S.Korea

At 2011-07-17 15:39:13,"Eyvaz Isaev" <eyvaz_isaev at yahoo.com> wrote:

> I was not sure whether this problem caused by empty-band number, so I increase nbnd.
> 
>You should increase nbnd if you see "too few bands" message  in *.ph.out file. 
>
>Bests,
>Eyvaz. 
> 
>
> 
>
>
>________________________________
>From: GAO Zhe <flux_ray12 at 163.com>
>To: Eyvaz Isaev <eyvaz_isaev at yahoo.com>; PWSCF Forum <pw_forum at pwscf.org>
>Sent: Sunday, July 17, 2011 11:33 AM
>Subject: Re: [Pw_forum] ph.x cannot reach convergence within 100 steps
>
>
>Thank you very much, Prof. Isaev.
>I tried all of 'scf', 'relax' and 'vc-relax' before ph.x, but got the same problem in each case~
>I was not sure whether this problem caused by empty-band number, so I increase nbnd. It may too large for my model~ Now, I am trying to change the values of alpha_mix(1) and nmix_ph for a better convergent.
>Thank you, again ^_^
>
>--
>GAO Zhe
>CMC Lab, MSE, SNU, Seoul, S.Korea
>
>At 2011-07-16 16:39:40，"Eyvaz Isaev" <eyvaz_isaev at yahoo.com> wrote:
>
>Hi, 
>>
>>
>>
>>>Recently, I am trying to calculate phonon dispersion via ph.x. However, 
in some cases, ph.x cannot reach convergence within 100 steps and stop 
>automaticly.
>> 
>>1. You should  perform 'scf', not 'vc-relax' before phonon calculations.
>>2. You have a rather large system (nbnd=100), but used alpha_mix(1) by default (0.7). Try it around 0.1.
>>3. Try changing nmix_ph (by default 4).
>>4. If this does not help change 'maxter=100' in phcom.f90 and recompile.
>>
>>Bests,
>>Eyvaz.
>>
>>
>>-------------------------------------------------------------------
>>Prof. Eyvaz Isaev, 
>>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
>>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
>>isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>
>>
>>________________________________
>>From: GAO Zhe <flux_ray12 at 163.com>
>>To: PWSCF Forum <pw_forum at pwscf.org>
>>Sent: Saturday, July 16, 2011 7:40 AM
>>Subject: [Pw_forum] ph.x cannot reach convergence within 100 steps
>>
>>
>>Dear QE developer and users:
>>Recently, I am trying to calculate phonon dispersion via ph.x. However, in some cases, ph.x cannot reach convergence within 100 steps and stop automaticly.
>>I have tested the convergent lattice parameter, cut-off energy and k-points (M-P grid), and the thresholds of force and stress were also very low. Even if I increase the tr2_ph from
 1.0d-12 (default) to 1.0d-10, the |ddv_scf|^2  values was around 10^(-6) or 10^(-7) magnitude. The problem usually occurred at the second q-point, but sometimes, even if lucky enough, it would definitely occur at
 the third q-point (4 q-points in 3x3x3 case).
>>Are there any methods to solve this problem? Any suggestion will be welcome.
>>Calculations were used GGA-PBE USPP.
>>This is my input file:
>>cat >W25.relax.in <<EOF
>>&control
>>     calculation = 'vc-relax' ,
>>     disk_io = 'low' ,
>>     prefix = 'W' ,
>>     outdir = '$TempDIR/' ,
>>     pseudo_dir = '$PseudoDIR/' ,
>>     etot_conv_thr = 1.0d-12 ,
>>     forc_conv_thr = 1.0d-4 ,
>>/
>>&system
>>     ibrav = 1 ,
>>     celldm(1) = ******* ,
>>     nat = ** ,
>>     ntyp = 3 ,
>>     nbnd = 100 ,
>>     ecutwfc = 47.5 ,
>>     ecutrho = 450 ,
>>     occupations =
 'smearing' ,
>>     smearing = 'mp' ,
>>     degauss = 0.003 ,
>>/
>>&electrons
>>     conv_thr = 1.0d-12 ,
>>     startingpot = 'atomic' ,
>>     startingwfc = 'atomic+random' ,
>>     diagonalization = 'cg' ,
>>     electron_maxstep = 150 ,
>>/
>>&ions
>>     ion_dynamics = 'bfgs' ,
>>/
>>&cell
>>     cell_dynamics = 'bfgs' ,
>>     press_conv_thr = 0.01 ,
>>/
>>ATOMIC_SPECIES
>>  V   50.9415   V.pbe-n-van.UPF
>>  W   183.800   W.pbe-nsp-van.UPF
>>  C   12.0110   C.pbe-van_ak.UPF
>>ATOMIC_POSITIONS crystal
>>  V   0.50  0.50  0.00
>>...........
>>  C   0.50  0.50  0.50
>>K_POINTS
 automatic
>>13  13  13   0  0  0
>>EOF
>>echo -e "  Relaxing Structure...\c"
>>$MPIBIN/mpirun -n 6 pw.x -npool 2 <W.relax.in >W.relax.out
>>echo -e " DONE"
>>
>>cat >W.ph.in <<EOF
>>Phonon Calculation
>>&inputph
>>     outdir = '$TempDIR/' ,
>>     prefix = 'W' ,
>>     ldisp = .true. ,
>>     nq1 = 3 ,
>>     nq2 = 3 ,
>>     nq3 = 3 ,
>>     tr2_ph = 1.0d-10 ,
>>     fildyn = 'W.dyn' ,
>>/
>>EOF
>>echo -e "  Calculating Dynamic Matrix...\c"
>>$MPIBIN/mpirun -n 6 ph.x -npool 2 <W.ph.in >W.ph.out
>>echo -e " DONE"
>>
>>
>>
>>--
>>GAO Zhe
>>CMC Lab, MSE, SNU, Seoul, S.Korea
>>
>>
>>
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>>Pw_forum mailing list
>>Pw_forum at pwscf.org
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>>
>>
>>
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