[Pw_forum] Graphene Phonons Not Working

[Abualnaja, Faris]

To whom it may concern,


I've been having trouble lately trying to produce graphene phonon dispersion plots. I am currently using quantum-espresso/5.0.2. I ran an scf calculation using an LDA norm conserving pseudo potential (C.pz-vbc.UPF). I found an optimised lattice parameter of 4.698 (Bohr) using a vc-relax calculation. I then ran an scf with the optimised lattice parameter and ecutwfc. I then proceeded onto producing a band structure with the following k-points in units of 2pi/a (Gamma (0,0,0) - K (0.33333, 0.57735027, 0) - M (0.5, 0.28867513, 0)). The band structure agrees with literature, where the dirac points meet at the K point. I then moved on to calculating the phonon at each k (or q) point. I ran the scf calculation once again in a new directory, I ran the phonon at gamma, K, and M. the results seemed to agree with literature. However, when I ran the phonon dispersion calculation, the results go all over the place. The gamma k and m points are the same but the curve is not expected. Obviously, after running the ph.x I ran a q2r.x calculation, followed by a matdyn.x calculation. To be clear I checked my k-points, I checked the k-path, the mp grid I used was 12x12x1 when calculating the phonon dispersion and 48x48x1 when running an scf calculation. Also, to clarify I did the tutorial for Al and Si and produced correct plots. Below are my input files:

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-------- SCF ---------------------------------------------------------------------------------------------------------------------

&CONTROL

  prefix         = 'graphene'

  pseudo_dir     = '/home/fa2215/bin/upf_files'

  calculation    = 'scf'

  restart_mode   = 'from_scratch'

  verbosity      = 'high'

  tprnfor        = .TRUE.

  tstress        = .TRUE.

  etot_conv_thr  = 1.0D-4

  forc_conv_thr  = 1.0D-3

  nstep          = 50000

  wf_collect     = .TRUE.

/


&SYSTEM

  ibrav            = 4

  celldm(1)        = 4.698

  celldm(3)        = 18.616

  nat              = 2

  ntyp             = 1

  nbnd             = 10

  ecutwfc          = 110

  ecutrho          = 440

  occupations      = 'smearing'

  smearing         = 'mp'

  degauss          = 0.1

/


&ELECTRONS

  diagonalization   = 'david'

  electron_maxstep  = 1000

  conv_thr          = 1.0e-8

  mixing_beta       = 0.3

/


ATOMIC_SPECIES

  C 12.01 C.pz-vbc.UPF

ATOMIC_POSITIONS crystal

  C         0.6666666666  0.3333333333  0.0000000000

  C         0.3333333333  0.6666666666  0.0000000000

K_POINTS (automatic)

48 48 1  0 0 0

------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------------------------

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------ PHONON ---------------------------------------------------------------------------------------------------------------------

Phonon Dispersion of graphene

 &inputph

  tr2_ph=1.0d-12

  ldisp=.true.

  nq1=12 nq2=12 nq3=1

  prefix='graphene'

  amass(1)=12.01

  outdir='/work/fa2215/Computational_Data/Graphene/Flat_Graphene/NM_PZ_LDA/Phonon_Calc/Disp/Disp2'

  fildyn='graphene.dyn'

 /

------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------------------------

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----------- Q2R --------------------------------------------------------------------------------------------------------------------

&input

    fildyn='graphene.dyn', zasr='crystal', flfrc='graphene.fc'

/

------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------------------------

-------- MATDYN -------------------------------------------------------------------------------------------------------------------

&input

    asr='crystal'

    amass(1)=12.01

    flfrc='graphene.fc'

    flfrq='graphene.freq'

/

 219

    0.000000    0.000000    0.000000   1.0

         :                    :                    :                :

------------------------------------------------------------------------------------------------------------------------------------


So to recap my procedure was as follows:


scf

phonon disp

q2r

matdyn


Let me know if anything is unclear and thank you for your help!


Best,


Faris


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