[QE-users] Discrepancy between QE and VASP when including Efield in slab system

[Carlos Polanco Garcia]

Dear all



*Problem in brief:* My calculations of the change in the bandgap with
electric filed in bilayer MoS2 using Quantum Espresso (QE) version 5.4.0 do
not agree with similar calculations in the literature that used VASP.



*Questions:*

   1. Have anyone found discrepancies of the change of dispersion with
   electric filed from QE and VASP in slab systems including Electric fields
   with the sawtooth potential?
   2. Is there any problem with my input?



*Details of the simulation:* An input for bilayer MoS2 with an Electric
field of 2V/nm is below. I set the discontinuity of the sawtooth potential
to be in vacuum and I set the magnitude of the electric filed using the
conversion factor 1 a.u. = 51.4220632*10^10 V/m.



&control

  calculation='scf',

  outdir = '/home/tmp/MoS2.2L.E2.01/'

  prefix='MoS2.2L',

 pseudo_dir = '/home/pseudo/',

  restart_mode='from_scratch',

  tprnfor=.true.

  tefield=.true.

/

&system

  ibrav=4,

  celldm(1)=    6.02820958

  celldm(3)=   6.629172038

  nat=6,

  ntyp= 2,

  ecutwfc=  80.0,

  nbnd=24

  vdw_corr='DFT-D'

  edir=3

  eamp =   0.00388938

  emaxpos=0.60

  eopreg=0.10

/

&electrons

  conv_thr= 1.0d-9,

  mixing_beta= 0.6,

/



ATOMIC_SPECIES

  Mo  95.94    Mo.pbe-mt_fhi.UPF

  S   32.065   S.pbe-mt_fhi.UPF



ATOMIC_POSITIONS {alat}

  Mo       0.000000000   0.000000000   0.000000000

  S        0.500000000   0.288675135  -0.492491069

  S        0.500000000   0.288675135   0.492515463

  Mo       0.500000000   0.288675135   1.969804069

  S       -0.000000000  -0.000000000   1.477442788

  S       -0.000000000  -0.000000000   2.462449934



K_POINTS {automatic}

  13 13 1 0 0 0



*Details of the problem:* Overall the dispersion for Efield=0 agrees
decently with other calculations in the literature including those using
VASP. However when I increase the electric field, my calculations predict a
change in the Bandgap with electric field about four times weaker than that
predicted from VASP calculations. For instance, from E0=0V/nm to E2=2V/nm,
my bandgap (Gamma to K) decreases by 0.19 eV. On the other hand, similar
VASP calculations predict that the bandgap decreases by 0.89 eV (Figure 2,
red dispersions from [1]), and by 0.73 eV (Figure 5a from [2]). My
calculations agree better with calculations that do not relay on VASP. An
independent calculation with QE predicts a similar slope in the change of
Bandgap with Efield for Efileds larger than 1V/nm (red dots Fig 3a [3]). A
calculation with Siesta predicts a decrease in bandgap of 1.04 eV when
increasing Efiled from 0V/nm to 5V/nm (Fig 4 b,d orange lines [4]), while
my calculations predict a change in bandgap of 0.78 eV (20% difference).
The agreement of the dispersions at Efield=0V/nm points that the problem is
in how the Efiled is being included. My input for QE may be missing
something, or there may be a factor difference in how Efield is included
between VASP and QE.



*References:*

[1] Ramasubramaniam A. et al, “Tunable band gaps in bilayer
transition-metal dichalcogenides”, PHYSICAL REVIEW B 84, 205325 (2011)

[2] Chu T. et al, “Electrically Tunable Bandgaps in Bilayer MoS2”, Nano
Lett. 2015, 15, 8000−8007

[3] Nguyen C. et al, “Band Gap Modulation of Bilayer MoS2 Under Strain
Engineering and Electric Field: A Density Functional Theory”, Journal of
ELECTRONIC MATERIALS, Vol. 45, No. 8, 2016

[4] Santos E., et al, “Electrically Driven Tuning of the Dielectric
Constant in MoS2 Layers”, ACS NANO, VOL. 7,  NO. 12,  10741–10746 ’ 2013



Carlos Polanco

Scientist at Sivananthan Laboratories


-- 
Carlos Andrés Polanco García
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20210308/6531b7e3/attachment.html>