[Pw_forum] Phonon frequencies could not converge of ENCUT by version 5.2.

[黄志硕]

Dear all users,


I encountered one problem when doing consistency test of parameters of
phonon frequencies at Gamma point, shown as in the Table below, in which
are the lowest phonon frequencies of Gamma point after applying ASR.


>From the table, we can see that for smearing (S (Ry)), the frequency
converge well except smearing=0.125Ry, which is understandable because of
the too large value of smearing.  The problem part is the convergence of
ENCUT. In general, the larger ENCUT is, the better results are. But for
higher ENCUT, it does not converge. Could anyone give me any instructions
why the convergent of ENCUT is like this, I will appreciate it.


The K-mesh is 4*4*4 which turns out OK for the system and all of structures
are well relaxed under the parameters. And the calculations are carried out
by Quantum Espresso-5.2.



ENCUT/(Ry)
    40 45 50 55 60 65 70
S
(Ry) 0.005 -67.2 -0.37 -0.37 -127.84 -0.28 -0.25 -87.94
0.010 -66.91 -0.37 -0.37 -127.88 -0.26 -0.25 -87.88
0.025 -67.57 -0.35 -0.38 -127.69 -0.31 -0.26 -87.93
0.125 -- -2196.53  -2273.29  -22497.9  -2203.83  -3215.92  -2258.14​

The input file of the scf calculation is shown below:
########################################
 &control
    calculation='scf'
    restart_mode='from_scratch',
    prefix='K3C60',
    pseudo_dir = './',
    outdir='./',
    tstress = .true.
    tprnfor = .true.
 /
 &system
    ibrav= 2, celldm(1)= 26.9097, nat=63, ntyp=2, nbnd=137
    ecutwfc = 70, ecutrho = 280
    occupations='smearing', smearing='gaussian', degauss=0.005
 /
 &electrons
    mixing_beta = 0.7, conv_thr = 1.0D-10
 /
 &ions
    ion_dynamics = 'damp'
 /
ATOMIC_SPECIES
 C  12  C.pbe-mt.UPF
 K  39.1  K.pbe-mt_norel.UPF
ATOMIC_POSITIONS (angstrom)
C        1.167584737   3.033367455   1.424268580
C        0.721014984   2.305670430   2.591830404
C       -0.721014984   2.305670430   2.591830404
.
.
.
K_POINTS automatic
4 4 4 1 1 1
########################################
With the phonon calculation input file:
########################################
Phonon of K3C60
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  recover=.true.
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
 /
0.0 0.0 0.0
########################################

Best regards

Zhishuo Huang
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