[QE-users] Phonon–EPW Discrepancy in MoS2 Calculations near Gamma Point

[Vahid Askarpour]

For EPW calculations, I generally use the lifc tag (see EPW documentation) which utilizes the force constants generated by the q2r.x. The EPW phonon dispersion then will match that of matdyn.x.

Best,
Vahid

Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University
Halifax, Canada

On Nov 5, 2025, at 4:25 AM, sally issa <sally.issa1 at outlook.com> wrote:

CAUTION: The Sender of this email is not from within Dalhousie.
Dear Quantum ESPRESSO Team,
I am performing phonon and EPW calculations for monolayer MoS2 using Quantum ESPRESSO and EPW. After applying the acoustic sum rule (ASR), the phonon dispersion from matdyn.x looks correct and physically consistent.
However, when comparing these results with the phonon frequencies interpolated in EPW, I observe a negative frequency near the Gamma point that does not appear in the matdyn.x results.
Could you please advise what might cause this discrepancy and how I can improve the simulation to achieve better agreement between the two?
Attached are my input files for the ph.x, matdyn.x, and epw.x runs for reference.
Thank you for your time and your support.
Kind regards,
Sally Issa
Q2r.in:
&input
 fildyn = '/scratch/MoS2/phonons/MoS2.dyn',
 zasr = 'crystal',
 flfrc = './MoS2.espresso.ifc2'
 write_lr = .true.
 loto_2d=.true.
/
Ph.in:
&inputph
  prefix   = 'MoS2',
  amass(1) = 95.95,
  amass(2) = 32.065,
  outdir   = '/scratch/MoS2/phonons/ph661-input'
  fildyn   = '/scratch/MoS2/phonons/MoS2.dyn'
  ldisp    = .true.,
  recover = .true.,
  epsil     = .true.
  fildvscf = 'dvscf',
  nq1=6,
  nq2=6,
  nq3=1,
  tr2_ph   =  1.0d-13
 /
Epw.in:

&inputepw
  prefix      = 'MoS2'
  outdir      = '/scratch/MoS2/epw/epw_dir_q661_k18181/'
  amass(1)    = 95.95        ! Mo
  amass(2)    = 32.065       ! S

  elph        = .true.
  kmaps       = .false.
  epbwrite    = .true.
  epbread     = .false.

  !ephwrite    = .true.
  epwwrite    = .true.
  epwread     = .false.

  etf_mem     = 1

  ! polar/2D long-range treatment
  lpolar      = .true.
  system_2d   = .true.       ! v5.3 accepts logical; (string choices arrive later)
  asr_typ = 'crystal'

  !band subspace / excluded bands for Wannierization
  nbndsub     = 11
  bands_skipped = 'exclude_bands = 1:6'  ! exclude first 6 bands from wannierization

  ! internal wannierization (uses libwannier90)
  wannierize  = .true.
  num_iter    = 1000
  dis_win_min = -10
  dis_win_max =   4
  dis_froz_min= -10
  dis_froz_max=   3
  proj(1)     = 'Mo:d'
  proj(2)     = 'S:p'

  ! pass-through to wannier90 via wdata
  wdata(1)  = 'bands_plot = .true.'
  wdata(2)  = 'begin kpoint_path'
  wdata(3)  = 'G 0.000 0.000 0.000   K 0.333333333 0.333333333 0.0000000'
  wdata(4)  = 'K 0.333333333 0.333333333 0.0000000   M 0.5 0.0 0.000000'
  wdata(5)  = 'M 0.5 0.0 0.000000     G 0.0 0.0 0.0'
  wdata(6)  = 'end kpoint_path'
  wdata(7)  = 'bands_plot_format = gnuplot'
  wdata(8)  = 'guiding_centres = .true.'
  wdata(9)  = 'kmesh_tol = 1.0e-6'
  wdata(10) = 'search_shells = 40'

  iverbosity  = 0

  !self-energies / Eliashberg off
  elecselfen  = .false.
  phonselfen  = .false.
  a2f         = .false.

  !Fermi level control
  efermi_read = .true.
  fermi_energy= -1.7901      ! eV

  !plotting along paths (EPW will read filkf/filqf when band_plot=.true.)
  band_plot   = .true.
  dvscf_dir   = '/scratch/MoS2/phonons/ph661-input/save'
  filkf       = './highsymkpts.txt'
  filqf       = './highsymkpts.txt'

  nk1 = 18
  nk2 = 18
  nk3 = 1

  nq1 =  6
  nq2 =  6
  nq3 = 1
/
<matdyn.in><disp_qeandelphbolt.png><disp.pdf>_______________________________________________________________________________
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