[QE-users] wrong phonon dispersion at K-point

[Roozbeh Anvari]

Dear Quantum Espresso experts,

I am having a trouble calculating the phonon bands of graphene at
$K$-point,

I am using NC+LDA and NC+PBE, ecutwfs=60, Ecutrho=400.0,
forc_conv_thr=1.0d-6,

as you can see in the attached figure, the calculated acoustic and optical
eigenvalues are ok at $\Gamma$ and $M$-points, however the calculated value
deviates from what it should be at $K$-point:
TA and ZA branches are not overlapping at $K$-point,
and a strange bump can be seen when ZO approaches $K$-point,

I have checked the convergence for K-mesh, Ecutwfs, and Ecutrho,
I have also tried increasing the K and q mesh for scf-calculation,
using tr2_ph = 1E-14 and alpha_mix(niter)= .1 also does not improve the
results,


Thank you for your help,
Regards,
Roozbeh
PDF, physics, Queen's university


Here is the setup I am using,

    step 1, pw.x

    &CONTROL
    ....
     calculation='scf'
     forc_conv_thr=1.0d-6,
    /

    &SYSTEM
    ibrav=0, nat = 2, ntyp = 1,
    ecutwfc = 60.0 , ecutrho = 400.0, ! 480
    nosym=.true.,
    occupations='smearing', smearing='cold', degauss=0.02
    la2F = .true.,
   /

    &ELECTRONS
    startingwfc='random'
    diagonalization='cg'
    conv_thr = 1.0e-12
    mixing_beta = 0.2
    electron_maxstep=200


    ATOMIC_SPECIES
    C  12.011   C.pz-vbc.UPF

    CELL_PARAMETERS (angstrom)
       2.428479517  -0.000000605   0.000000000
      -1.214240282   2.103124989   0.000000000
       0.000000000   0.000000000  20.000000000

    ATOMIC_POSITIONS (crystal)
    C            -0.0002315717        0.0002344099        0.4996978700
    C             0.6664267343        0.3335704066        0.4996978902

    K_POINTS automatic
    64 64  1 0 0 0

    %--------------------
    %      step 2 ,pw.x
    %--------------------

  same as above except
  la2F = .false.,
   K_POINTS automatic
    32 32 1 0 0 0

    %--------------------
    %      step 3 , ph.x
    %--------------------


     &inputph
      tr2_ph=1.0d-14,
      prefix='ml_gr',
      fildvscf='ml_gredv',
      amass(1)=12.011,
      outdir='./tmp',
      fildyn='ml_gr.dyn',
      electron_phonon='interpolated',
      !el_ph_sigma=0.005,
      !el_ph_nsigma=10,
      alpha_mix=0.1
      diagonalization='cg',
      trans=.true.,
      ldisp=.true.,
      nq1=4 , nq2=4, nq3=1
      ! nq1=8 , nq2=8, nq3=1   makes no difference
     /


    %--------------------
    %      step 4  , q2r.x
    %--------------------

     &input
      zasr='simple',
      fildyn='ml_gr.dyn',
      flfrc='gr333.fc',
      la2F=.true.
     /


    %--------------------
    %      step 5 , matdyn.x
    %--------------------

      &input
        asr='simple',
        amass(1)=12.011,
        flfrc='gr333.fc',
        flfrq='gr333.freq',
        la2F=.true.,
        dos=.false.
         q_in_band_form=.true.
 /
       4
        0 0 0 20
        0 .5 0 20
       -0.3333333  0.6666666  0. 20
        0 0 0 1
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20210123/4fa0948e/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 60_400_64_32_4.png
Type: image/png
Size: 66340 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20210123/4fa0948e/attachment.png>