[Pw_forum] grid phonon calculation at non-gamma point cannot reach convergence

[Isaiah Moses]

Hi Yuan,
Your structure seems big, many nbnd.
For such structure, smaller value of alpha_mix(1) in phonon input is
helpful for convergence.
Non inclusion of alpha_mix(1) in your input file implies that the default
value of 0.7 would be used.
Include alpha_mix(1) and use smaller value such as 0.2.

If that doesn't solve the problem, you may need to increase the convergence
threshold tr2_ph.

It is also helpful to split your job along the q-points. This will enable
you monitor the convergence of different q-point and adjust parameters such
as alpha_mix(1) and tr2_ph accordingly.

Best,
Isaiah

On Mon, Oct 2, 2017 at 12:51 PM, yuan liang <yl4ps at virginia.edu> wrote:

> Dear QE developers and users,
>
> Recently I'm trying to calculate phonon dos via ph.x, however, although I
> can get fine convergence result at gamma point, ph.x cannot reach
> convergence within 100 steps and stop automaticly at the 1st non gamma
> point on my mesh.
>
> The material is YVO3, orthorhombic, with 4 Y atom, 4 V atom and 12 O atom
> per unit cell.
>
> The QE version is 5.4.0
>
> I tried both GGA PBEsol USPP and LDA USPP(from THEOS SSSP)
>
> Are there any methods to solve this problem? Any suggestion will be welcome.
>
> Here are my input files:
> *scf calculation*
> &control
>    calculation= 'scf',
>    restart_mode= 'from_scratch',
>    prefix='YVO3_exc',
>    pseudo_dir = '...',
>    outdir= '...',
>    wf_collect=.true.,
>    tprnfor=.true., tstress=.true.
> /
> &system
>  ibrav = 8,
>  celldm(1) = 9.9893,
>  celldm(2) = 1.0581,
>  celldm(3) = 1.4296,
>  nat = 20,
>  ntyp = 3,
>  ecutwfc = 60,
>  ecutrho = 480,
>  ecfixed = 60,
>  qcutz = 20,
>  q2sigma = 5,
>  occupations= 'smearing', smearing='gauss', degauss=0.01,
> /
> &electrons
>  mixing_beta = 0.4,
>  mixing_mode = 'plain',
>  conv_thr = 1.0d-10,
> /
> ATOMIC_SPECIES
>  Y 88.906 y_lda_v1.4.uspp.F.UPF
>  V 50.942 v_lda_v1.4.uspp.F.UPF
>  O 15.999 o_lda_v1.2.uspp.F.UPF
> ATOMIC_POSITIONS crystal
>  Y 0.97830 0.07150 0.25000
>  ...
>  O 0.18720 0.20040 0.55663
> K_POINTS automatic
>  6 6 4 0 0 0
> *phonon calculation on grid*
> &inputph
>  prefix='YVO3_exc',
>  outdir='...',
>  recover=.true.,
>  *ldisp=.true*.,
>  nq1=6,
>  nq2=6,
>  nq3=4,
>  tr2_ph=1.0d-14,
>  fildyn='YVO3_dyn.G',
>  amass(1)=80.906,
>  amass(2)=50.942,
>  amass(3)=15.999,
> /
> 0.000000 0.000000 0.000000
>
> Best regards,
>
> Yuan Liang
> Physics Department,
> University of Virginia
>
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>



-- 
Isaiah Abu Moses
Graduate Student,
Physics Department,
University of Ibadan,
Nigeria
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