[Pw_forum] convergence problem in phonon calculation

[Ari P Seitsonen]

Dear "yangxunscience at 163.com", (sorry for the missing character set)

   Have you understood which kind of pseudo potentials you have chosen to 
use with Quantum ESPRESSO? In particular going from the PAW (most likely, 
or ultra-soft pp's) to the FHI pp's shown in your input? Did you check 
that the cut-off energy for the wave functions, 'ecutwfc', is sufficient? 
I doubt so, if not already for Cr. In principle you do not need to set the 
'ecutrho' for the norm-conserving pp's, and do you have a reason to give 
an explicit value of 'nbnd' if your system does have a large band gap (I 
conclude this because your mixing parametre is loose and you do not use 
fractional occupation numbers and still get a converged electronic 
structure)?

   Once you are well converged in the cut-off energy, you probably want to 
relax both the lattice constants and the ionic positions once more with 
the present pp's; otherwise your phonon eigenvalues and -vectors are not 
that precise because you are not at the minimum of the potential energy 
surface, whereas this is assumed (harmonically) when calculating the 
phonons.

     Good Luck,

        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


On Wed, 13 May 2015, 杨顶峰 wrote:

> Dear All,
> 
>                 I am trying the quantum espresso 5.1 to perform the phonon
> calculation of a compound.
> firstly, i use VASP to get a better geometry calculation , then the opted
> model was used to carried out the self consistent calculation and phonon
> calculation on quantum espresso 5.1 .
> my input file for the self consistent calculation  is given below:
> &control
>    title='sbcrse3'
>    calculation = 'scf' ,
>    restart_mode='from_scratch',
>    wf_collect=.true.,
>    prefix = 'sbcrse3',
>    outdir = './',
>    pseudo_dir = './',
>    tstress=.true.
>    tprnfor=.true.
>    etot_conv_thr=1.0D-6,
>    forc_conv_thr=1.0D-6,
> /
> 
> &system
>    ibrav = 8,
>    celldm(1) = 17.721473993588537072269931508765,
>    celldm(2) = 0.40987224478027270642574239356715,
>    celldm(3) = 1.4354965598661794909645534975973,
>    nat = 20 ,
>    ntyp = 3 ,
>    ecutwfc = 40,
>    ecutrho = 300,
>    occupations = 'fixed' ,
>    nbnd = 150,
> /
> 
> &electrons
>    mixing_beta=0.7
>    conv_thr = 1.0d-10 ,
> /
> 
> ATOMIC_SPECIES
>   Sb    121.7       Sb.pbe-mt_fhi.UPF
>   Se    78.96       Se.pbe-mt_fhi.UPF
>   Cr    51.996      Cr.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
> Sb     0.471599996         0.250000000         0.655629992
> Sb     0.528400004         0.750000000         0.344370008
> Sb     0.028400004         0.750000000         0.155629992
> Sb     0.971599996         0.250000000         0.844370008
> .....
> 
> K_POINTS automatic
>   13 13 13   0  0  0
> 
> the above calculation was running successfully. the details shows as
> follows:
> 
> 
> convergence has been achieved in  76 iterations
> 
>      Forces acting on atoms (Ry/au):
> 
>      atom    1 type  1   force =     0.00330300   -0.00000173    0.01711914
>      atom    2 type  1   force =    -0.00330300    0.00000173   -0.01711914
>      atom    3 type  1   force =    -0.00330300    0.00000173    0.01711914
>      atom    4 type  1   force =     0.00330300   -0.00000173   -0.01711914
>      atom    5 type  2   force =    -0.00590819   -0.00028964    0.01684058
>     ........
> 
>      Total force =     0.064539     Total SCF correction =     0.000006
> 
> 
>      entering subroutine stress ...
> 
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
>  -77.36
>   -0.00044232   0.00000132   0.00000000        -65.07      0.19      0.00
>    0.00000132  -0.00068747   0.00000000          0.19   -101.13      0.00
>    0.00000000   0.00000000  -0.00044787          0.00      0.00    -65.88 
> 
> But when i begin the phonon calculation there is a problem, some tips will
> be show in the "out " file:
> Electric Fields Calculation
>      ik   1 ibnd  59 linter: root not converged  5.993E-09
>      ik   1 ibnd  59 linter: root not converged  3.084E-09
>      ik   2 ibnd  59 linter: root not converged  2.722E-07
>      ik   2 ibnd  59 linter: root not converged  3.810E-09
>      ik   2 ibnd  59 linter: root not converged  1.129E-09
>      ik   3 ibnd  59 linter: root not converged  1.634E-09
>      ik   3 ibnd  59 linter: root not converged  9.282E-09
>      ik   3 ibnd  59 linter: root not converged  1.749E-09
>      ik   4 ibnd  59 linter: root not converged  2.191E-09
>      ik   4 ibnd  59 linter: root not converged  2.338E-09
>      ik   4 ibnd  59 linter: root not converged  1.895E-09
>      ik   5 ibnd  59 linter: root not converged  1.241E-08
>      ik   5 ibnd  59 linter: root not converged  1.440E-09
>      ik   5 ibnd  59 linter: root not converged  3.946E-09
>      ik   6 ibnd  59 linter: root not converged  5.932E-08
>      ik   6 ibnd  59 linter: root not converged  6.026E-09
>      ik   6 ibnd  59 linter: root not converged  5.804E-08
>      ik   7 ibnd  59 linter: root not converged  6.012E-09
>      ik   7 ibnd  59 linter: root not converged  1.088E-09
>      ik   7 ibnd  59 linter: root not converged  1.407E-08
>      ik   8 ibnd  59 linter: root not converged  1.962E-09
> ................
> the calculation is still on progress, i really don`t know how to conquer the
> problem as a new beginner, please help me, Thanks a lot!
> 
> 
> 
>