[QE-users] speed up the phonon calculation of large cells

[sha.liu]

Dear experts and developers,

I am calculating the phonon DOS of several large cells (30~90 atoms per 
unit cell). I found the calculation took too much time and if there is 
anything wrong, I need to wait at least I got some results. Could you 
give me some advice on how to speed up the calculation? Also, I found 
for most cases, the phonon calculation can not reach the convergence. 
One of my scf input and ph input is like this:

&CONTROL
title = 'Mg2Zn11',
prefix = 'Mg2Zn11',
calculation = 'vc-relax',
restart_mode = 'from_scratch',
pseudo_dir = '../',
outdir = './tmp',
forc_conv_thr = 1d-5,
nstep = 300,
/
&SYSTEM
ecutwfc = 80.0,
ibrav = 1,
celldm(1) = 16.1581354,
nat = 39,
ntyp = 2,
occupations = 'smearing',
smearing = 'gaussian',
degauss = 0.011,
use_all_frac = .true.
/
&ELECTRONS
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
  Mg  24.305  Mg.pbe-spnl-rrkjus_psl.1.0.0.UPF
  Zn  65.409  Zn.pbe-dnl-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS crystal
   Mg    0.302470  0.000000  0.500000
   Mg    0.500000  0.302470  0.000000
   Mg    0.000000  0.500000  0.302470
   Mg    0.500000  0.697530  0.000000
   Mg    0.000000  0.500000  0.697530
   Mg    0.697530  0.000000  0.500000
   Zn    0.500000  0.500000  0.500000
   Zn    0.229963  0.000000  0.000000
   Zn    0.000000  0.229963  0.000000
   Zn    0.000000  0.000000  0.229963
   Zn    0.000000  0.770037  0.000000
   Zn    0.000000  0.000000  0.770037
   Zn    0.770037  0.000000  0.000000
   Zn    0.159837  0.500000  0.000000
   Zn    0.000000  0.159837  0.500000
   Zn    0.500000  0.000000  0.159837
   Zn    0.000000  0.840163  0.500000
   Zn    0.500000  0.000000  0.840163
   Zn    0.840163  0.500000  0.000000
   Zn    0.218205  0.218205  0.218205
   Zn    0.781795  0.781795  0.218205
   Zn    0.218205  0.781795  0.781795
   Zn    0.218205  0.781795  0.781795
   Zn    0.781795  0.218205  0.781795
   Zn    0.781795  0.781795  0.781795
   Zn    0.218205  0.218205  0.781795
   Zn    0.781795  0.218205  0.218205
   Zn    0.218205  0.781795  0.218205
   Zn    0.500000  0.235252  0.341765
   Zn    0.341765  0.500000  0.235252
   Zn    0.235252  0.341765  0.500000
   Zn    0.764748  0.658235  0.500000
   Zn    0.341765  0.500000  0.764748
   Zn    0.764748  0.341765  0.500000
   Zn    0.658235  0.500000  0.235252
   Zn    0.658235  0.500000  0.764748
   Zn    0.235252  0.658235  0.500000
   Zn    0.500000  0.764748  0.658235
   Zn    0.500000  0.235252  0.658235
   Zn    0.500000  0.764748  0.341765

K_POINTS automatic
   8 8 8 1 1 1


&inputph
   tr2_ph=1.0d-16,
   prefix='Mg2Zn11',
   amass(1)= 24.305,
   amass(1)= 65.409,
   outdir='./tmp',
   fildyn='Mg2Zn11.dyn',
   ldisp=.true.,
   nq1=4, nq2=4, nq3=4,
  /


Regards,
Sha Liu
IMDEA Materials Institute
C/Eric Kandel 2, Getafe 28906-Madrid, Spain