[QE-users] Wrong position of fermi level in bulk Cr2O3
Nicola Marzari
nicola.marzari at epfl.ch
Thu Jul 23 14:38:22 CEST 2020
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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--
----------------------------------------------------------------------
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
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