[Pw_forum] Nd2Fe14B Magnetization
Kurth, Michael R.
kurth.17 at buckeyemail.osu.edu
Tue Jun 17 04:02:41 CEST 2014
Dear Juanjo,
Thank you for the advice. We did try a DFT+U calculation only on the neodymium atoms, but it was also with the default number of bands. We saw similar results in terms of total magnetization as the other calculations we ran without the +U correction.
Thanks,
Michael
Graduate Student in Nuclear Engineering
Department of Mechanical and Aerospace Engineering
The Ohio State University
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On Behalf Of Juanjo Meléndez
Sent: Monday, June 16, 2014 1:37 PM
To: PWSCF Forum
Subject: Re: [Pw_forum] Nd2Fe14B Magnetization
Dear Michael
I think that the problem is the presence of Nd in your lattice. As far as I know, f-electrons are not only tricky to handle within a DFT formalism, but they constitute the border of its validity. I would not expect a great degree of accuracy in your calculations for any PP you may use.
Anyway, you could try with DFT+U with the proper correction for correlated f-electrons (and maybe d-electrons from Fe as well). Sometimes it is hard to converge, but it could help. Anyway, I would not expect any miracle.
BTW. Do not waste your time trying to change ecutrho. You are using a norm-conserving pseudopotential, so that ecutrho is meaningless.
Good luck
Juanjo
Juan J. Meléndez
Associate Professor
Department of Physics · University of Extremadura
Avda. de Elvas, s/n 06006 Badajoz (Spain)
Phone: +34 924 28 96 55
Fax: +34 924 28 96 51
Email: melendez at unex.es
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html
From: Kurth, Michael R.<mailto:kurth.17 at buckeyemail.osu.edu>
Sent: Monday, June 16, 2014 5:52 PM
To: PWSCF Forum<mailto:pw_forum at pwscf.org>
Subject: Re: [Pw_forum] Nd2Fe14B Magnetization
Dear Dr. Rebaza,
Thank you for the reply. We did increase ecutrho to approximately 6 times the ecutwfc value and did not see a notable difference in the calculation. As far as the value of ecutwfc=260, we arrived at this value after running calculations at ecutwfc=300 and not observing a 1 mRy/atom difference in the total energy. We also have tested PBE and PW pseudopotentials but have not observed a difference in the total magnetization value.
Sincerely,
Michael Kurth
Graduate Student in Nuclear Engineering
Department of Mechanical and Aerospace Engineering
The Ohio State University
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On Behalf Of Arles V. Gil Rebaza
Sent: Monday, June 16, 2014 11:28 AM
To: PWSCF Forum
Subject: Re: [Pw_forum] Nd2Fe14B Magnetization
Dear Michael, are you sure that "ecutwfc = 260.0" is a enough value for your system, may be you should increse, and you're using the default value of "ecutrho", try to converge with this tag.!!!
Best
PhD. Arles V. GIl Rebaza
Instituto de Física La Plata
La Plata - Argentina
2014-06-16 12:16 GMT-03:00 Kurth, Michael R. <kurth.17 at buckeyemail.osu.edu<mailto:kurth.17 at buckeyemail.osu.edu>>:
Hello,
I am trying to calculate the magnetization of NdFeB which is a ferromagnetic material and a metal. This calculation has been done before using different methods than plane waves and pseudopotentials. Moreover, the magnetization per formula unit has been experimentally measured. The previous calculations and experimental values agree and report a magnetization per formula unit of around 37 Bohr Magneton. The previous calculations used the Generalized Gradient Approximation for the exchange correlation functional.
We first tried the calculation using the default number of bands and the input file is attached below:
&control
calculation='scf'
restart_mode='from_scratch',
wf_collect=.TRUE.,
prefix='NdFeB',
pseudo_dir = '/usr/local/espresso/espresso-5.0.3/pseudo/',
outdir = '/fs/lustre/osu7834/NdFeB/'
/
&system
ibrav=0, nat=68, ntyp=3,
nspin=2, starting_magnetization(1)=0.6, starting_magnetization(2)=0.6, starting_magnetization(3)=0.6,
ecutwfc = 260.0
occupations='smearing', smearing='mv', degauss=0.002
/
&electrons
conv_thr=1.0e-6
mixing_beta=0.02
mixing_mode = 'local-TF'
/
CELL_PARAMETERS {angstrom}
8.8 0.0 0.0
0.0 12.19 0.0
0.0 0.0 8.8
ATOMIC_SPECIES
Nd 144.24 Nd.pbe-mt_fhi.UPF
Fe 55.845 Fe.pbe-mt_fhi.UPF
B 10.811 B.pbe-mt_fhi.UPF
ATOMIC_POSITIONS {angstrom}
B 5.54400 0.00000 3.25600
B 3.25600 0.00000 5.54400
B 7.65600 6.09500 7.65600
B 1.14400 6.09500 1.14400
Fe 4.40000 0.00000 0.00000
Fe 4.40000 6.09500 0.00000
Fe 0.00000 6.09500 4.40000
Fe 0.00000 0.00000 4.40000
Fe 4.40000 1.37747 4.40000
Fe 0.00000 7.47247 0.00000
Fe 0.00000 4.71753 0.00000
Fe 4.40000 10.81253 4.40000
Fe 0.85360 2.49895 0.85360
Fe 7.94640 2.49895 7.94640
Fe 5.25360 8.59395 3.54640
Fe 3.54640 8.59395 5.25360
Fe 5.25360 3.59605 3.54640
Fe 3.54640 3.59605 5.25360
Fe 0.85360 9.69105 0.85360
Fe 7.94640 9.69105 7.94640
Fe 2.79840 3.01093 2.79840
Fe 6.00160 3.01093 6.00160
Fe 7.19840 9.10593 1.60160
Fe 1.60160 9.10593 7.19840
Fe 7.19840 3.08407 1.60160
Fe 1.60160 3.08407 7.19840
Fe 2.79840 9.17907 2.79840
Fe 6.00160 9.17907 6.00160
Fe 4.99840 1.56032 1.97120
Fe 3.80160 1.56032 6.82880
Fe 6.37120 7.65532 8.20160
Fe 2.42880 7.65532 0.59840
Fe 0.59840 4.53468 2.42880
Fe 8.20160 4.53468 6.37120
Fe 1.97120 10.62968 4.99840
Fe 6.82880 1.56032 3.80160
Fe 3.80160 10.62968 6.82880
Fe 4.99840 10.62968 1.97120
Fe 2.42880 4.53468 0.59840
Fe 6.37120 4.53468 8.20160
Fe 8.20160 7.65532 6.37120
Fe 0.59840 7.65532 2.42880
Fe 6.82880 10.62968 3.80160
Fe 1.97120 1.56032 4.99840
Fe 3.15920 2.14544 0.34320
Fe 5.64080 2.14544 8.45680
Fe 4.74320 8.24044 1.24080
Fe 4.05680 8.24044 7.55920
Fe 7.55920 3.94956 4.05680
Fe 1.24080 3.94956 4.74320
Fe 0.34320 10.04456 3.15920
Fe 8.45680 2.14544 5.64080
Fe 5.64080 10.04456 8.45680
Fe 3.15920 10.04456 0.34320
Fe 4.05680 3.94956 7.55920
Fe 4.74320 3.94956 1.24080
Fe 1.24080 8.24044 4.74320
Fe 7.55920 8.24044 4.05680
Fe 8.45680 10.04456 5.64080
Fe 0.34320 2.14544 3.15920
Nd 2.34080 0.00000 2.34080
Nd 6.45920 0.00000 6.45920
Nd 6.74080 6.09500 2.05920
Nd 2.05920 6.09500 6.74080
Nd 7.56800 0.00000 1.23200
Nd 1.23200 0.00000 7.56800
Nd 5.63200 6.09500 5.63200
Nd 3.16800 6.09500 3.16800
K_POINTS {automatic}
4 4 4 0 0 0
This input file was prepared after checking convergence with respect to the energy cutoff and the number of points and did converge after 2 restart runs. Unfortunately, we obtained a magnetization of 25 Bohr Magneton/f.u. (which is too small).
Furthermore, and after checking for convergence with respect to the number of bands (by adding more bands) we found that we end up with a magnetization of 50 Bohr Magneton/f.u. (which is too big).
I also think that the degauss value used for smearing is small enough and can't be the problem.
Are there any recommendations for what other parameters I could examine to help me get the right answer?
Your help is greatly appreciated!
Sincerely,
Michael Kurth
Graduate Student in Nuclear Engineering
Department of Mechanical and Aerospace Engineering
The Ohio State University
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