[Pw_forum] Nd2Fe14B Magnetization

Pang Rui pang.r at sustc.edu.cn
Tue Jun 17 13:50:18 CEST 2014


Maybe you can check if different starting magnetizations converge into
one. 

On Tue, 17 Jun 2014 02:02:41 +0000, "Kurth, Michael R."
<kurth.17 at buckeyemail.osu.edu> wrote:
> 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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> 
> 
> 
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-- 
PostDoc
Department of Physics, South University of Science and Technology of China



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