[QE-users] Strange phonons frequencies with spin included

[Qiyuan Ruan]

Dear developers,
Recently I was trying phonon calculations with spin, and was getting strange results, so I went down to one carbon atom in vacuum expecting frequencies to be close to zero. However, it seems that results vary a lot giving frequency -51 cm^-1 for C.pz-n-kjpaw_psl.0.1.UPF pseudopotential, and ~900-1000 cm^-1 with C.pbe-van_bm.UPF pseudopotential. Otherwise the calculation seems to be running fine, so there is no way of knowing if there is a problem or not. I am using version 6.0 and including my inputs and excerpts from output. Kindly please help me resolve this if you have any insights. Thank you!

Qiyuan Ruan


SCF input:
scf.in
&control
    calculation='scf'
    etot_conv_thr = 1.d-11,
    verbosity='high',
/
 &system
    nat=1, ntyp=1,
    ibrav=0,
    ecutwfc=60.0, occupations='smearing', degauss = 0.01, smearing='mp',
    la2F = .true.,
    nspin = 2,
    starting_magnetization(1) = 1,
    nosym =.true.,
 /
 &electrons
    mixing_beta = 0.5,
    mixing_mode = 'local-TF'
    conv_thr =  1.0d-12,
 /
ATOMIC_SPECIES
 C  12.01 C.pz-n-kjpaw_psl.0.1.UPF
CELL_PARAMETERS  angstrom
10.000000000000000 0.000000000000000 0.000000000000000
0.000000000000000 10.000000000000000 0.000000000000000
0.000000000000000 0.000000000000000 10.000000000000000
ATOMIC_POSITIONS crystal
C 0.5 0.5 0.5
K_POINTS automatic
1 1 1 0 0 0

Phonon input:

&inputph
  tr2_ph=1.0d-17,
  alpha_mix(1)=0.3,
  amass(1)=12.01,
  niter_ph=500,
  trans=.true.,
  ldisp=.true.,
  nq1=1, nq2=1, nq3=1,
  start_q=1,
  last_q=1,
 /

Output for C.pz-n-kjpaw_psl.0.1.UPF:

Diagonalizing the dynamical matrix

     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     freq (    1) =      -1.543361 [THz] =     -51.480967 [cm-1]
     freq (    2) =      -1.540965 [THz] =     -51.401048 [cm-1]
     freq (    3) =      -1.538275 [THz] =     -51.311315 [cm-1]
***************************************************************************
Output for C.pbe-van_bm.UPF:

Diagonalizing the dynamical matrix

     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     freq (    1) =      26.838049 [THz] =     895.220954 [cm-1]
     freq (    2) =      30.156019 [THz] =    1005.896529 [cm-1]
     freq (    3) =      30.677843 [THz] =    1023.302678 [cm-1]
 **************************************************************************


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