[Pw_forum] Nd2Fe14B Magnetization

Juanjo Meléndez melendez at unex.es
Mon Jun 16 19:37:10 CEST 2014


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. 
Sent: Monday, June 16, 2014 5:52 PM
To: PWSCF Forum 
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>:

 

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 0.00.0 12.19 0.00.0 0.0 8.8ATOMIC_SPECIESNd  144.24   Nd.pbe-mt_fhi.UPFFe  55.845   Fe.pbe-mt_fhi.UPF               B   10.811   B.pbe-mt_fhi.UPF          ATOMIC_POSITIONS {angstrom}B       5.54400     0.00000     3.25600B       3.25600     0.00000     5.54400B       7.65600     6.09500     7.65600B       1.14400     6.09500     1.14400Fe      4.40000     0.00000     0.00000Fe      4.40000     6.09500     0.00000Fe      0.00000     6.09500     4.40000Fe      0.00000     0.00000     4.40000Fe      4.40000     1.37747     4.40000Fe      0.00000     7.47247     0.00000Fe      0.00000     4.71753     0.00000Fe      4.40000    10.81253     4.40000Fe      0.85360     2.49895     0.85360Fe      7.94640     2.49895     7.94640Fe      5.25360     8.59395     3.54640Fe      3.54640     8.59395     5.25360Fe      5.25360     3.59605     3.54640Fe      3.54640     3.59605     5.25360Fe      0.85360     9.69105     0.85360Fe      7.94640     9.69105     7.94640Fe      2.79840     3.01093     2.79840Fe      6.00160     3.01093     6.00160Fe      7.19840     9.10593     1.60160Fe      1.60160     9.10593     7.19840Fe      7.19840     3.08407     1.60160Fe      1.60160     3.08407     7.19840Fe      2.79840     9.17907     2.79840Fe      6.00160     9.17907     6.00160Fe      4.99840     1.56032     1.97120Fe      3.80160     1.56032     6.82880Fe      6.37120     7.65532     8.20160Fe      2.42880     7.65532     0.59840Fe      0.59840     4.53468     2.42880Fe      8.20160     4.53468     6.37120Fe      1.97120    10.62968     4.99840Fe      6.82880     1.56032     3.80160Fe      3.80160    10.62968     6.82880Fe      4.99840    10.62968     1.97120Fe      2.42880     4.53468     0.59840Fe      6.37120     4.53468     8.20160Fe      8.20160     7.65532     6.37120Fe      0.59840     7.65532     2.42880Fe      6.82880    10.62968     3.80160Fe      1.97120     1.56032     4.99840Fe      3.15920     2.14544     0.34320Fe      5.64080     2.14544     8.45680Fe      4.74320     8.24044     1.24080Fe      4.05680     8.24044     7.55920Fe      7.55920     3.94956     4.05680Fe      1.24080     3.94956     4.74320Fe      0.34320    10.04456     3.15920Fe      8.45680     2.14544     5.64080Fe      5.64080    10.04456     8.45680Fe      3.15920    10.04456     0.34320Fe      4.05680     3.94956     7.55920Fe      4.74320     3.94956     1.24080Fe      1.24080     8.24044     4.74320Fe      7.55920     8.24044     4.05680Fe      8.45680    10.04456     5.64080Fe      0.34320     2.14544     3.15920Nd      2.34080     0.00000     2.34080Nd      6.45920     0.00000     6.45920Nd      6.74080     6.09500     2.05920Nd      2.05920     6.09500     6.74080Nd      7.56800     0.00000     1.23200Nd      1.23200     0.00000     7.56800Nd      5.63200     6.09500     5.63200Nd      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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