[QE-users] Inconsistency in electronic band structure of GeP3 monolayer

[Marcelo Albuquerque]

Dear users,

I'm trying to calculate the electronic band structure of GeP3, but I
haven't been able to reproduce it, as shown in both references below.

a) Bowen Zeng et al 2018 J. Phys. D: Appl. Phys. 51 235302;
b) Yu Jing, et al, Nano Lett. 2017, 17, 3, 1833–1838.

BTW, they were computed using VASP code, and I don't understand why I'm
facing such an issue. I have already tried many different approaches to
calculate this band structure, but it simply doesn't work.

Here follows the inputs I used for the scf and the bands calculations.

A) SCF
&control
    prefix='gep',
    calculation='scf'
    nstep=0
    tstress=.false.
    tprnfor= .true.
    etot_conv_thr = 1.0D-5
    forc_conv_thr = 1.0D-7
    pseudo_dir = '/home/malbuquerque/pseudos/',
    outdir='./'
 /
 &system
    ibrav=  4,
a=  6.982664008,
c = 16.000000000,
nat= 8,
 ntyp= 2,
ecutwfc = 120,
 nbnd = 40
       vdw_corr='grimme-d2'
        occupations='fixed',
/
&electrons
electron_maxstep = 400
conv_thr = 1.0d-12
diagonalization='david'
mixing_mode='plain'
mixing_beta= 0.7
 /
&ions
ion_dynamics='bfgs'
/
&CELL
  cell_dynamics = 'bfgs',
   press_conv_thr = 0.5,
   cell_factor = 2.0,
   cell_dofree = '2Dxy',
/
ATOMIC_SPECIES
Ge  72.640   Ge.pbe-hgh.UPF
P   30.974   P.pbe-hgh.UPF
ATOMIC_POSITIONS crystal
Ge       0.836927687   0.360474777   0.413486925
Ge       0.503586578   0.693798663   0.359352022
P        0.325445130   0.871903831   0.425075713
P        0.859830506   0.871910609   0.425081984
P        0.325454709   0.337550097   0.425072126
P        0.014988446   0.182362365   0.347653353
P        0.014997809   0.716639703   0.347643675
P        0.480752135   0.182372957   0.347659202
K_POINTS automatic
13 13 1 0 0 0


B) BANDS
&control
    prefix='gep',
    calculation='bands'
    nstep=0
    tstress=.false.
    tprnfor= .true.
    etot_conv_thr = 1.0D-5
    forc_conv_thr = 1.0D-7
    pseudo_dir = '/home/malbuquerque/pseudos/',
    outdir='./'
 /
&system
ibrav=  4,
a=  6.982664008,
c = 16.000000000,
nat= 8,
 ntyp= 2,
ecutwfc = 120,
 nbnd = 40
       vdw_corr='grimme-d2'
        occupations='fixed',
 /
 &electrons
electron_maxstep = 400
conv_thr = 1.0d-12
diagonalization='david'
mixing_mode='plain'
mixing_beta= 0.7
 /
&ions
ion_dynamics='bfgs'
/
&CELL
  cell_dynamics = 'bfgs',
   press_conv_thr = 0.5,
   cell_factor = 2.0,
   cell_dofree = '2Dxy',
/
ATOMIC_SPECIES
Ge  72.640   Ge.pbe-hgh.UPF
P   30.974   P.pbe-hgh.UPF
ATOMIC_POSITIONS (crystal)
Ge       0.836927687   0.360474777   0.413486925
Ge       0.503586578   0.693798663   0.359352022
P        0.325445130   0.871903831   0.425075713
P        0.859830506   0.871910609   0.425081984
P        0.325454709   0.337550097   0.425072126
P        0.014988446   0.182362365   0.347653353
P        0.014997809   0.716639703   0.347643675
P        0.480752135   0.182372957   0.347659202
K_POINTS crystal_b
4
0.000000000    0.000000000    0.000000000  30 !! Gamma
0.333333333    0.333333333    0.000000000  30 !! K
0.500000000    0.000000000    0.000000000  30 !! M
0.000000000    0.000000000    0.000000000  30 !! Gamma



In fact, I used the the QE versions6.7, 6.6 and 6.4.1, which gave me the
same strange result. I'm also sending a PNG file showing the obtained
bands. The red line is the VBM, and the blue one is the CBM (or it was
supposed to be). What is weird is that I was expecting (according to the
aforementioned reference) that the blue band was located a little bit above
where it is in this figure. Also the orange one should be a little bit
above, close to the VBM.

Could anyone help me or give me some advice about this problem. I really
appreciate it in advance.


With all the best regards,

Marcelo Albuquerque

Ph.D. Candidate

Institute of Physics

Fluminense Federal University
Niterói/RJ - Brazil
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