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

[Giovanni Cantele]

Hi Marcelo,

I do not see an evident reason why you should find a discrepancy. However, by looking to Fig. 1b of the first reference and to the side view of you structure (as obtained by opening the scf input directly with XcrysDEN), it seems to me that there is some difference in the z coordinates. Also, I tried (but I don’t know if in the correct way) to calculate "the puckered height between P–P and Ge–Ge” as mentioned in the reference. Again, your structure seems to be different. Did you relax the structure before making the scf? What is the value of “Total force” at the end of the scp output?

Giovanni

PS is there any reason why not trying with PAW pseudo potentials requiring a much smaller cutoff?
(this has of course nothing to do with your issue)

> On 20 Jul 2021, at 17:42, Marcelo Albuquerque <marcelofilho at id.uff.br> wrote:
> 
> 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
> <bandsGeP3_pw-users.png>_______________________________________________
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