[QE-users] Need some suggestion regarding the band gap issue of Fe3O4
Iurii TIMROV
iurii.timrov at epfl.ch
Mon Nov 15 17:24:39 CET 2021
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
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