[QE-users] Need some suggestion regarding the band gap issue of Fe3O4
Giuseppe Mattioli
giuseppe.mattioli at ism.cnr.it
Mon Nov 15 17:51:40 CET 2021
Dear K C Bhamu
On top of Iurii's consderations, if you calculate a linear-response U
value for Fe, then the U correction makes the energy functional
locally linear with respect to the number of electrons and, therefore,
it opens a local gap between occupied and unoccupied electronic
states, which are coupled to the other, uncorrected valence states.
This does not mean that you are applying a global correction to the
band gap problem, i.e., you are not globally linearizing the energy
functional with respect to the number of electrons but in a few lucky
cases. In the case of TM oxides, for example, not applying some
correction to O 2p states may lead to an undesired overstabilization
of occupied metal 3d orbitals wrt O 2p ones, with unpredictable
effects on the materials properties. If you want to mitigate the
problem without messing up with semiempirical approaches you should
use either DFT+U+V (but read everything carefully before choosing
arbitrary values) or a hybrid EXX functional (very easy to use with NC
pseudopotentials, affordable in the case of your system but clearly
much more expensive than GGA or DFT+U).
HTH
Giuseppe
Quoting Iurii TIMROV via users <users at lists.quantum-espresso.org>:
> Dear K C Bhamu,
>
>
>> Do you think my input file (see below) has any issues? I have
>> defined all tetra-Fe sites dn-spin and all octahedra Fe sites
>> up-spin.
>
>
> I recommend to check with the QE input generator:
> https://www.materialscloud.org/work/tools/qeinputgenerator
>
>
>> What other things I should take care of to reproduce the band gap
>> (0.14 eV to 0.3 eV)?
>
>
> I never studied this system but I can give general comments:
>
> - you can try to determine Hubbard parameters using the HP code of QE
>
> - you can try to use "ortho-atomic" Hubbard projectors instead of
> "atomic" (U_projection_type): https://www.mdpi.com/2076-3417/11/5/2395
>
> - maybe try DFT+U+V?
> https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.104402 (see Fig. 6) Tutorial:
> https://www.youtube.com/watch?v=WSABAqPWNH0&t=5s
>
>
>> In the research paper
>> [3]<https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202>, the
>> authors used VASP and the valence configuration for the Fe atom was
>> taken as 3d64s1. I could not find any PP from the list I mention
>> below which has this configuration. Does this may be an issue? If
>> anyone has PP of Fe with 3d64s1 configuration, please provide me.
>
>
> Check SSSP: https://www.materialscloud.org/discover/sssp/table/efficiency
>
>
> HTH
>
>
> Iurii
>
>
> --
> Dr. Iurii TIMROV
> Senior Research Scientist
> Theory and Simulation of Materials (THEOS)
> Swiss Federal Institute of Technology Lausanne (EPFL)
> CH-1015 Lausanne, Switzerland
> +41 21 69 34 881
> http://people.epfl.ch/265334
> ________________________________
> From: users <users-bounces at lists.quantum-espresso.org> on behalf of
> Dr. K. C. Bhamu <kcbhamu85 at gmail.com>
> Sent: Monday, November 15, 2021 11:47:16 AM
> To: Quantum Espresso users Forum
> Subject: [QE-users] Need some suggestion regarding the band gap
> issue of Fe3O4
>
> Dear QE Users,
>
> This email may be large for you all as I am trying to put all the
> information so that I do not miss any information in your response.
> I sincerely apologize for this long email.
>
>
> I am dealing with ferrimagnetic Fe3O4 (with QE6.6) and trying to
> reproduce its band gap. In the literature, its experimental band gap
> was reported to be in the range of 0.14-0.3eV, Table SI-1
> [1]<https://aip.scitation.org/doi/10.1063/1.5138941> for the up-spin
> state. For Fe3O4 nanoparticles, the band gap is reported ~2eV.
>
> I have tried with all available PPs (mentioned below in different
> sets) and U values from 1eV to 7eV. At lower U (=1-2eV), I am
> getting this system a direct band-gap half-metal (a gap is opened in
> the spin-up channel) and with increasing the U value, the direct
> band-gap (=~1eV) nature changes to the indirect (=~2eV) band gap. At
> U=7eV with the rrkjus PPs, it showed a metallic character.
>
> I have also carried out the band structure, by keeping the lattice
> parameters fixed at experimental values and only relaxing ionic
> position, with varying U-values. But still, the nature of the
> bang-gap is similar to what I just mentioned above(band gap varies
> from ~1eV to ~2eV with U=1eV to 7eV, respectively).
>
> The lattice parameters, magnetic moments, and the charge on Fe_tet
> and Fe_oct sites I am getting reasonably in accordance with the
> Table SI-1<https://aip.scitation.org/doi/10.1063/1.5138941>.
>
> A sample of my input file is also shown below (the only PPs are
> different with respective cutoffs).
>
> Information collected from other research papers:
> 1. See
> [2]<https://www.sciencedirect.com/science/article/abs/pii/S0039602812000544>
> (In section 3.1. Bulk Fe3O4: 0.33 eV band gap with VASP with
> U=3.8eV ).
> 2. See
> [3]<https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202>
> (Page-4, bottom left para: 2.1 eV using VASP with U=4 eV). This
> paper only shows the direct band-gap of 2.1eV.
> Based on my already finished calculations and the details that I
> have covered above, I have a few queries:
>
> 1. Do you think my input file (see below) has any issues? I have
> defined all tetra-Fe sites dn-spin and all octahedra Fe sites up-spin.
> 2. What other things I should take care of to reproduce the band
> gap (0.14 eV to 0.3 eV)?
> 3. In the research paper
> [3]<https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202>, the
> authors used VASP and the valence configuration for the Fe atom was
> taken as 3d64s1. I could not find any PP from the list I mention
> below which has this configuration. Does this may be an issue? If
> anyone has PP of Fe with 3d64s1 configuration, please provide me.
> 4. As mentioned in the research paper
> [4]<https://pubs.acs.org/doi/full/10.1021/acs.jpcc.7b09387>, the
> authors have mentioned that "Our results show that, upon releasing
> the symmetry constraint on the density but not on the geometry,
> charge disproportionation (Fe2+/Fe3+) is observed, resulting in a
> band gap of around 0.2 eV at the Fermi level." How can I release
> symmetry constrain on the density? I used nonsym=True also but the
> calculation was not converging in this case.
>
> Supporting information for this email:
>
> Combinations of my PPs:
>
> Set-1 (ecutwfc/ecutrho = 40/320Ry)
> Fe.pbe-nd-rrkjus.UPF
> O.pbe-rrkjus.UPF
>
> Set-2 (ecutwfc/ecutrho = 45/450Ry)
> Fe.pbe-sp-van_mit.UPF
> O.pbe-rrkjus.UPF
>
> Set-3 (ecutwfc/ecutrho = 65/785Ry) >> similar to yours
> Fe.pbe-spn-rrkjus_psl.1.0.0.UPF
> O.pbe-n-rrkjus_psl.1.0.0.UPF
>
> set-4 (ecutwfc/ecutrho = 64/782Ry)
> Fe.pbe-spn-kjpaw_psl.0.2.1.UPF
> O.pbe-n-kjpaw_psl.0.1.UPF
>
> QE input file:
>
> &CONTROL
> calculation = 'scf'
> etot_conv_thr = 1.0000000000d-04
> forc_conv_thr = 1.0000000000d-03
> ! disk_io = 'none'
> outdir = './tmp/'
> prefix = 'pwscf'
> pseudo_dir = '~/PPs/'
> ! tprnfor = .true.
> ! tstress = .true.
> ! verbosity = 'high'
> /
> &SYSTEM
> degauss = 0.01
> ecutrho = 785
> ecutwfc = 65
> ibrav = 0
> nat = 56
> nosym = .false. !! I have tried with .True. also but my
> calculations were not converging.
> ntyp = 3
> occupations = 'smearing' , smearing = 'mp'
> starting_magnetization(1) = 1
> starting_magnetization(2) = -1
> nspin = 2
> lda_plus_u=.true.
> Hubbard_U(1)=X (tried 1eV to 7eV)
> Hubbard_U(2)=X (tried 1eV to 7eV)
>
>
> /
> &ELECTRONS
> conv_thr = 1.000000000d-6
> electron_maxstep = 200
> mixing_beta = 3.0000000000d-01
> /
> &IONS
> ion_dynamics = 'bfgs'
> /
> &CELL
> /
>
> ATOMIC_SPECIES
> Fe1 55.845 Fe.pbe-spn-rrkjus_psl.1.0.0.UPF
> Fe2 55.845 Fe.pbe-spn-rrkjus_psl.1.0.0.UPF
> O 15.9994 O.pbe-n-rrkjus_psl.1.0.0.UPF
> ATOMIC_POSITIONS crystal
> Fe1 0.6250000000 0.6250000000 0.6250000000
> Fe1 0.6250000000 0.3750000000 0.3750000000
> Fe1 0.3750000000 0.6250000000 0.3750000000
> Fe1 0.3750000000 0.3750000000 0.6250000000
> Fe1 0.6250000000 0.8750000000 0.8750000000
> Fe1 0.8750000000 0.6250000000 0.8750000000
> Fe1 0.8750000000 0.8750000000 0.6250000000
> Fe1 0.6250000000 0.1250000000 0.1250000000
> Fe1 0.1250000000 0.6250000000 0.1250000000
> Fe1 0.1250000000 0.1250000000 0.6250000000
> Fe1 0.1250000000 0.3750000000 0.8750000000
> Fe1 0.1250000000 0.8750000000 0.3750000000
> Fe1 0.3750000000 0.1250000000 0.8750000000
> Fe1 0.8750000000 0.1250000000 0.3750000000
> Fe1 0.3750000000 0.8750000000 0.1250000000
> Fe1 0.8750000000 0.3750000000 0.1250000000
> Fe2 0.0000000000 0.0000000000 0.0000000000
> Fe2 0.2500000000 0.2500000000 0.2500000000
> Fe2 0.0000000000 0.5000000000 0.5000000000
> Fe2 0.5000000000 0.0000000000 0.5000000000
> Fe2 0.5000000000 0.5000000000 0.0000000000
> Fe2 0.2500000000 0.7500000000 0.7500000000
> Fe2 0.7500000000 0.2500000000 0.7500000000
> Fe2 0.7500000000 0.7500000000 0.2500000000
> O 0.3750000000 0.3750000000 0.3750000000
> O 0.3750000000 0.6250000000 0.6250000000
> O 0.6250000000 0.3750000000 0.6250000000
> O 0.6250000000 0.6250000000 0.3750000000
> O 0.8750000000 0.8750000000 0.8750000000
> O 0.8750000000 0.6250000000 0.6250000000
> O 0.6250000000 0.8750000000 0.6250000000
> O 0.6250000000 0.6250000000 0.8750000000
> O 0.3750000000 0.8750000000 0.8750000000
> O 0.8750000000 0.3750000000 0.8750000000
> O 0.8750000000 0.8750000000 0.3750000000
> O 0.3750000000 0.1250000000 0.1250000000
> O 0.8750000000 0.6250000000 0.1250000000
> O 0.8750000000 0.1250000000 0.6250000000
> O 0.6250000000 0.8750000000 0.1250000000
> O 0.1250000000 0.3750000000 0.1250000000
> O 0.1250000000 0.8750000000 0.6250000000
> O 0.6250000000 0.1250000000 0.8750000000
> O 0.1250000000 0.6250000000 0.8750000000
> O 0.1250000000 0.1250000000 0.3750000000
> O 0.8750000000 0.3750000000 0.3750000000
> O 0.3750000000 0.8750000000 0.3750000000
> O 0.3750000000 0.3750000000 0.8750000000
> O 0.8750000000 0.1250000000 0.1250000000
> O 0.3750000000 0.6250000000 0.1250000000
> O 0.3750000000 0.1250000000 0.6250000000
> O 0.6250000000 0.3750000000 0.1250000000
> O 0.1250000000 0.8750000000 0.1250000000
> O 0.1250000000 0.3750000000 0.6250000000
> O 0.6250000000 0.1250000000 0.3750000000
> O 0.1250000000 0.6250000000 0.3750000000
> O 0.1250000000 0.1250000000 0.8750000000
> K_POINTS automatic
> 3 3 3 0 0 0
> CELL_PARAMETERS angstrom
> 8.3840000000 0.0000000000 0.0000000000
> 0.0000000000 8.3840000000 0.0000000000
> 0.0000000000 0.0000000000 8.3840000000
>
>
>
> Thank you very much for having patience while going through this
> detailed email.
>
> I look forward to hearing from you.
>
>
> Regards
>
> K C Bhamu
> Postdoctoral Fellow
> School of Chemical Engineering
> University of Ulsan
> South Korea
GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>
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