[QE-users] Wrong position of fermi level in bulk Cr2O3

Yuvam Bhateja yuvamb16 at gmail.com
Thu Jul 23 18:00:50 CEST 2020


Thank you for the reply.

I am not sure how to solve this problem.
I tried using different pseudopotentials with diffrent XC. Even tried
increasing U value.

In most of the papers, pure bulk Cr2O3 is used.

Can you please advise me?

Thank you in advance.

Regards
Yuvam

On Thu, 23 Jul 2020, 6:08 pm Nicola Marzari, <nicola.marzari at epfl.ch> wrote:

>
>
> Indeed! Although I would feel better about using as Fermi energy the
> zero temperature limit of the chemical potential, that would be
> (homo+lumo)/2? (well, the band edges).
>
>                         nicola
>
> PS: of course the lumo is wrong even in exact DFT, and the homo is
> correct only in exact DFT, and wrong in approximate DFT.
>
> On 23/07/2020 14:35, Pietro Delugas wrote:
> > Dear Yuvam
> >
> > When  one uses smeared occupations in  systems with a  large gap (
> > significantly larger than the smearing) the final value of the Fermi
> > level returned from the calculation may be any value within the band gap
> > sufficiently far from the band edges (HOMO and LUMO).  All the  values
> > in this range yield the same values for the occupations and thus of the
> > ground state density.   If you wish you can decide to follow the
> > convention of the other papers and refer to the HOMO as the Fermi level.
> >
> > In fact in insulators the thermodynamic Fermi level depends on extrinsic
> > conditions such as doping or defect  concentrations and on the
> > temperature. All things which are obviously not taken into account in
> > your calculation.
> >
> > Kind regards
> >
> > Pietro
> >
> > Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> > Windows 10
> >
> > *From: *Yuvam Bhateja <mailto:yuvamb16 at gmail.com>
> > *Sent: *Thursday, July 23, 2020 12:44 PM
> > *To: *Quantum ESPRESSO users Forum <mailto:
> users at lists.quantum-espresso.org>
> > *Subject: *[QE-users] Wrong position of fermi level in bulk Cr2O3
> >
> > Hello dear experts,
> >
> > Hope you are doing well.
> >
> > I was trying to calculate the DOS in hexagonal Cr2O3, the DOS is coming
> > very well with a bandgap of 3.09, but the problem is the Fermi level is
> > at the edge of LUMO whereas I've observed that it should be at HUMO edge
> > in few already published papers.
> >
> > I used PBE NC SR pseudopotential and also optimized with the same. I
> > used gaussian smearing with a width of 0.001 in VC-relax and tetrahedra
> > in SCF calculation.
> >
> > Here is my input file -
> >
> > &CONTROL
> >      calculation   = "scf"
> >      pseudo_dir    = "./"
> >      outdir        = "./outdir"
> > /
> >
> > &SYSTEM
> >      a                         =  4.6166825e+00
> >      c                         =  1.2457778e+01
> >      ecutrho                   =  4.5000e+02
> >      ecutwfc                   =  4.5000e+01
> >      ibrav                     = 4
> >      nat                       = 30
> >      nspin                     = 2
> >      ntyp                      = 3
> >      nbnd                      = 276
> >      starting_magnetization(1) = 0.5
> >      starting_magnetization(2) = -0.5
> >      starting_magnetization(3) = 0.0
> >      tot_magnetization         = 0.0
> >      lda_plus_u                = .true.
> >      Hubbard_U(1)              = 4.7
> >      Hubbard_U(2)              = 4.7
> >      Hubbard_J0(1)             = 1
> >      Hubbard_J0(2)             = 1
> > /
> >
> > &ELECTRONS
> >      conv_thr         =  1.00000e-11
> >      electron_maxstep = 2000
> >      mixing_beta      =  7.00000e-01
> >      startingpot      = "atomic"
> >      startingwfc      = "atomic+random"
> > /
> >
> >
> > K_POINTS {automatic}
> >   12 12 12  0 0 0
> >
> > ATOMIC_SPECIES
> > Cr1    51.99610  Cr.upf
> > Cr2    51.99610  Cr.upf
> > O      15.99940  O.upf
> >
> > ATOMIC_POSITIONS (angstrom)
> > Cr2          -0.0000027528        2.6654550870        3.9638155751
> > Cr1           2.3083528721        1.3327252495        2.2651020880
> > Cr1          -0.0000027528        2.6654550870        0.1887989665
> > Cr2           0.0000000000        0.0000000000        1.8875092202
> > Cr2           0.0000000000        0.0000000000        8.1164268017
> > Cr1          -0.0000027528        2.6654550870        6.4177165986
> > Cr1           0.0000000000       -0.0000000000        4.3414084067
> > Cr2           2.3083528721        1.3327252495        6.0401185402
> > Cr2           2.3083528721        1.3327252495       12.2690363475
> > Cr1           0.0000000000        0.0000000000       10.5703258606
> > Cr1           2.3083528721        1.3327252495        8.4940197683
> > Cr2          -0.0000027528        2.6654550870       10.1927331413
> > O             1.4445126756        0.0000000398        3.1144588851
> > O             3.0306076646        0.0817435268        1.0381518347
> > O             0.8638388763        1.3327251470        1.0381518347
> > O             3.0306056520        2.5837116627        1.0381518347
> > O            -0.7222568310        1.2509851988        3.1144588851
> > O             1.5860942747        2.7471960155        3.1144588851
> > O             3.7528623252        1.3327254382        7.2670694393
> > O             0.7222547656        1.4144695631        5.1907658203
> > O            -1.4445122603        2.6654550733        5.1907658203
> > O             0.7222574947        3.9164369542        5.1907658203
> > O             1.5860961469        2.5837115564        7.2670694393
> > O             1.5860937210        0.0817433419        7.2670694393
> > O             1.4445122976        2.6654551364       11.4196834856
> > O            -1.5860942579        2.7471959172        9.3433763434
> > O             0.8638382678        3.9981804108        9.3433763434
> > O             0.7222569078        1.2509852624        9.3433763434
> > O            -0.7222575680        3.9164369549       11.4196834856
> > O            -0.7222547296        1.4144694992       11.4196834856
> >
> > I later tried with pw91 USPP, it fixed the fermi level position (it's
> > now at HUMO edge) but the bad gap is now very underestimated to 2.3 eV.
> >
> > I tried paw but it wasn't working with me.
> >
> > Can someone please help?
> >
> > Regards
> >
> > Yuvam Bhateja
> >
> > IIEST Shibpur
> >
> > India
> >
> >
> > _______________________________________________
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> )
> > users mailing list users at lists.quantum-espresso.org
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> >
>
>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
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