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I am having a trouble calculating the phonon band dispersion of graphene at $K$-point using Quantum-Espresso, using normconserving+LDA and normconserving+PBE, ecutwfs=60, Ecutrho=400.0, forc_conv_thr=1.0d-6,

as you can see in the 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, ()

Any help is appreciated, Cheers

Wrong phonon band dispersion of monolayer graphene

step 1, pw.x 

&CONTROL
 calculation='scf'
 title='ml_gr'
 prefix='ml_gr'
 verbosity='high'
 restart_mode= 'from_scratch'
 nstep=100
 tprnfor=.true.
 outdir='./tmp'
 disk_io='default'
 pseudo_dir='../pp_NC_LDA/'  ! LDA+NC
 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.
 /
58 ! number of q-points
0.          0.          0.
0.          0.02631579  0.
0.          0.05263158  0.
0.          0.07894737  0.
0.          0.10526316  0.
0.          0.13157895  0.
0.          0.15789474  0.
0.          0.18421053  0.
0.          0.21052632  0.
0.          0.23684211  0.
0.          0.26315789  0.
0.          0.28947368  0.
0.          0.31578947  0.
0.          0.34210526  0.
0.          0.36842105  0.
0.          0.39473684  0.
0.          0.42105263  0.
0.          0.44736842  0.
0.          0.47368421  0.
0.          0.5         0.
-0.01754386  0.50877193  0.
-0.03508772  0.51754386  0.
-0.05263158  0.52631579  0.
-0.07017544  0.53508772  0.
-0.0877193   0.54385965  0.
-0.10526316  0.55263158  0.
-0.12280702  0.56140351  0.
-0.14035088  0.57017544  0.
-0.15789474  0.57894737  0.
-0.1754386   0.5877193   0.
-0.19298246  0.59649123  0.
-0.21052632  0.60526316  0.
-0.22807018  0.61403509  0.
-0.24561404  0.62280702  0.
-0.26315789  0.63157895  0.
-0.28070175  0.64035088  0.
-0.29824561  0.64912281  0.
-0.31578947  0.65789474  0.
-0.33333333  0.66666667  0.
-0.31578947  0.63157895  0.
-0.29824561  0.59649123  0.
-0.28070175  0.56140351  0.
-0.26315789  0.52631579  0.
-0.24561404  0.49122807  0.
-0.22807018  0.45614035  0.
-0.21052632  0.42105263  0.
-0.19298246  0.38596491  0.
-0.1754386   0.35087719  0.
-0.15789474  0.31578947  0.
-0.14035088  0.28070175  0.
-0.12280702  0.24561404  0.
-0.10526316  0.21052632  0.
-0.0877193   0.1754386   0.
-0.07017544  0.14035088  0.
-0.05263158  0.10526316  0.
-0.03508772  0.07017544  0.
-0.01754386  0.03508772  0.
0.          0.          0.
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Adding q_in_cryst_coord=.true to the matdyn.x input file resolves the problem otherwise the code interprets the q-coordinates to be in Cartesian !

enter image description here

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