Re: [QE-users] Need some suggestion regarding the band gap issue of Fe3O4

2021-11-15 Thread Dr. K. C. Bhamu 
Dear Dr. Lurii,
Thank you for your important suggestions.
I have started HP code and got some errors which I have posted in a
separate email.
I am looking into more details and will get back to you with some updates.

Regards
Bhamu


On Mon, Nov 15, 2021 at 9:55 PM Iurii TIMROV via users <
users@lists.quantum-espresso.org> wrote:

> 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=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  on behalf of Dr.
> K. C. Bhamu 
> *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

Re: [QE-users] Need some suggestion regarding the band gap issue of Fe3O4

2021-11-15 Thread Giuseppe Mattioli 



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 :


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=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  on behalf of  
Dr. K. C. Bhamu 

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 al

Re: [QE-users] Need some suggestion regarding the band gap issue of Fe3O4

2021-11-15 Thread Iurii TIMROV via users 
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=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  on behalf of Dr. K. C. 
Bhamu 
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.

Support

[QE-users] Need some suggestion regarding the band gap issue of Fe3O4

2021-11-15 Thread Dr. K. C. Bhamu 
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]
 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
.

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]

(In section 3.1. Bulk Fe3O4: 0.33 eV band gap with VASP with U=3.8eV ).
2.  See [3]
   (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]
   , 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]
   , 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.UPFO.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:*


  calculation = 'scf'
  etot_conv_thr =   1.00d-04
  forc_conv_thr =   1.00d-03
!  disk_io= 'none'
  outdir = './tmp/'
  prefix = 'pwscf'
  pseudo_dir = '~/PPs/'
!  tprnfor = .true.
 ! tstress = .true.
!  verbosity = 'high'
/

  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)


/

  conv_thr =   1.0d-6
  electron_maxstep = 200
  mixing_beta =   3.00d-01
/

ion_dynamics = 'bfgs'
 /

/

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   0.625000   0.625000   0.625000
Fe1   0.625000   0.375000   0.375000
Fe1   0.375000   0.625000   0.375000
Fe1   0.375000   0.375000   0.625000
Fe1   0.625000   0.875000   0.875000
Fe1   0.875000   0.625000   0.875000
Fe1   0.875000