[Pw_forum] ecutrho in phonon calculations

[YY]

Dear all,

I am now calculating the phonon with ph.x (US-PP, off gamma point).
As recommended by the manual, ecutrho should be 8-10 times of ecutwfc.
 But I find there is no simple convergence trend while increasing
ecutrho.  When I use 35 Ry ecutwfc, and fix all the other parameters,
the results are like this:

   ecutrho       f1(cm-1)      ....  f12(cm-1)
   420            40.475                324.062
   600           123.746               350.727
   900           -251.876              306.721

I also increase ecutwfc, test the convergence of ecutrho, but get the
same trend.  So I don't know how to choose a "proper" ecutrho.

I attached the input files as following, and thanks for your help.

Yuyang,Ph.D student
RPI, USA


inputfile for the ph.x calculation:
 phonon
 &inputph
  tr2_ph=1.0d-14,
  prefix='yytest',
  amass(1)=55.845
  amass(2)=78.96
  outdir='./tmp'
  fildyn='yytest.dyn'
 /
0.000000000   0.200000000   0.000000000

inputfile for the SCF calculation
 &control
    calculation='scf'
    restart_mode='from_scratch',
    pseudo_dir='./'
    outdir='./tmp'
    prefix='yytest',
    tprnfor=.TRUE.
    tstress = .TRUE.
    wf_collect=.true.
 /
 &system
    ibrav=8, celldm(1)=7.18092, celldm(2)=1.000, celldm(3)= 1.515622236,
    nat= 4, ntyp=2,
    ecutwfc = 35
    ecutrho = 420
!    nbnd    = 24
    occupations = 'smearing',  smearing = 'gaussian',  degauss = 0.000736
 /
 &electrons
    conv_thr =  1.0d-10
 /
ATOMIC_SPECIES
 Fe  55.845   Fe.UPF
 Se  78.96    Se.UPF
ATOMIC_POSITIONS (crystal)
Fe       0.000000000   0.500000000   0.500000000
Fe       0.500000000   0.000000000   0.500000000
Se       0.000000000   0.000000000   0.726479503
Se       0.500000000   0.500000000   0.273520497
K_POINTS automatic
5 5 4 1 1 1