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Hi Yun-Peng<br>
<br>
If your objective is really to determine quantitatively the value of the magnetic anisotropy I think that it is an impossible task to get a precision of 0.01meV!!!<br>
<br>
Already below 0.1meV it is quite delicate but 0.01meV is just hopeless!<br>
<br>
Good luck<br>
Cyrille<br>
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<div style="font-family:Tahoma; font-size:13px"><b>Cyrille Barreteau</b><br>
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<font face="Times New Roman">(Dk)</font><br>
<font face="Times New Roman">email: cyrille.barreteau@cea.fr /</font><font face="Times New Roman">cyrbar@nanotech.dtu.dk<br>
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<div style="direction: ltr;" id="divRpF970161"><font face="Tahoma" color="#000000" size="2"><b>De :</b> pw_forum-bounces@pwscf.org [pw_forum-bounces@pwscf.org] de la part de peter [petercybertron@gmail.com]<br>
<b>Envoyé :</b> samedi 12 septembre 2015 23:33<br>
<b>À :</b> pw_forum@pwscf.org<br>
<b>Objet :</b> Re: [Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs<br>
</font><br>
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<div></div>
<div>Hi Cyrille,<br>
Since magnetic anisotropy energy is very small (~0.01 meV per atom in my system), do I need to use higher cutoff energies to account for such small energy scale?<br>
<br>
best,<br>
Yun-Peng<br>
<br>
<div class="moz-cite-prefix">On 09/12/2015 03:30 PM, BARRETEAU Cyrille wrote:<br>
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Dear Yun-Peng,<br>
<br>
>From experience I can just say that calculation using fully-relativistic PP can be really difficult to converge and sometimes almost impossible to achieve the desired accuracy (especially since magneto-crystalline anisotropy requires very strict convergence
thresholds). You can play with broadening and k points sampling.<br>
<br>
Cyrille<br>
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<div style="font-family:Tahoma; font-size:13px"><b>Cyrille Barreteau</b><br>
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New Roman">CEA Saclay<span style="background-color:white"></span></font><font face="Times
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</font><font face="Times
New Roman"><font face="Times
New Roman"><font face="Times
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SPEC</font></font><font face="Times
New Roman"><font face="Times
New Roman"><span style="background-color:white"> Bat. 771<br>
</span></font>91191 Gif sur Yvette Cedex<span style="background-color:white"></span>, FRANCE
<br>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~</font><br>
<font face="Times
New Roman">DTU Nanotech<br>
Ørsteds Plads, building 345E<br>
DK-2800 Kgs. Lyngby, DENMARK</font><br>
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(Dk)</font><br>
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cyrille.barreteau@cea.fr</a> /</font><font face="Times
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<div id="divRpF254260" style="direction:ltr"><font face="Tahoma" color="#000000" size="2"><b>De :</b>
<a class="moz-txt-link-abbreviated" href="mailto:pw_forum-bounces@pwscf.org" target="_blank">
pw_forum-bounces@pwscf.org</a> [<a class="moz-txt-link-abbreviated" href="mailto:pw_forum-bounces@pwscf.org" target="_blank">pw_forum-bounces@pwscf.org</a>] de la part de yuewen.fang [<a class="moz-txt-link-abbreviated" href="mailto:yuewen.fang@gmail.com" target="_blank">yuewen.fang@gmail.com</a>]<br>
<b>Envoyé :</b> samedi 12 septembre 2015 20:42<br>
<b>À :</b> pw_forum<br>
<b>Objet :</b> Re: [Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs<br>
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<div style="">Hi, Yun-Peng,
<div><br>
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<div>Thanks for your feedback. It depends on the matter which you are interested in. I think this paper (Phys. Rev. B 86, 085135 (2012)) can help you.
<div><br>
</div>
<div>Bests</div>
<div>Fang<br>
<br>
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<p class="MsoNormal"><span style="font-size:10pt" lang="EN-US"><font face="Georgia">Yue-Wen FANG, PhD candidate</font></span></p>
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<p class="MsoNormal"><span style="font-size:10pt" lang="EN-US"><font style="word-wrap:break-word" face="Georgia"><a href="http://english.ecnu.edu.cn/" style="word-wrap:break-word" target="_blank">East China Normal University</a></font></span></p>
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<div class="gmail_quote"><span dir="ltr">< <a href="mailto:petercybertron@gmail.com" target="_blank">
peter</a>> 2015-09-13 02:16:28 wrote: </span><br>
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<div>Thank you for your suggestions!<br>
I tried using a small mixing beta (0.1~0.2), and tried using reasonable cutoff energies (ecutwfc=50, ecutrho=500), now the convergence is much better than before (converged down to 10^-6 Ry).<br>
Another question is, I can find ultra-soft and PAW pseudopotentials, which one is better for spin-orbit calculations? I am using PBE XC functional.<br>
<br>
best,<br>
Yun-Peng<br>
<br>
<div class="moz-cite-prefix">On 09/11/2015 08:08 PM, yuewen.fang wrote:<br>
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<div style="">Dear Yun-Peng,
<div><br>
</div>
<div>Plz try to decrease mixing and perform some convergence tests for your cutoff energy to remove the oscillation of the energy! In addition, this oscillation could also be caused by the unreasonable smearing methods for metals.</div>
<div><br>
</div>
<div>Bests</div>
<div>Fang<br>
<br>
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<div><a href="http://www.yomail.com/?utm_source=signature" style="font-size:12pt" target="_blank">Sent from YoMail</a></div>
<br>
<div class="gmail_quote"><span dir="ltr">< <a href="mailto:petercybertron@gmail.com" target="_blank">
Peter Cybertron</a>> 2015-09-12 03:10:31 wrote:</span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex; border-left:1px #ccc solid; padding-left:1ex">
<div dir="ltr">Hi,<br>
<br>
<br>
I am working in University of Florida as a postdoc.<br>
I am exploring the spin-orbital calculations using pwscf, and I<br>
encounter a very slow convergence like this:<br>
> grep estimated scf.out<br>
estimated scf accuracy < 0.00000004 Ry<br>
... (100 similar lines)<br>
estimated scf accuracy < 0.00000003 Ry<br>
> grep "total energy" scf.out<br>
...<br>
total energy = -3667.91077719 Ry<br>
total energy = -3667.91078176 Ry<br>
total energy = -3667.91077642 Ry<br>
total energy = -3667.91078300 Ry<br>
<br>
<br>
Although the convergence of total energy seems OK (down to 0.00001 Ry ~<br>
0.0001 eV = 0.1 meV), I still feel uncomfortable since I never encounter<br>
such a problem without spin-orbit interactions.<br>
<br>
<br>
I downloaded the ultrasoft and PAW pseudopotentials from PSLib and I am<br>
using the PBE flavor of XC functional. The system I am studying is a two<br>
dimensional magnetic insulator.<br>
<br>
<br>
The parameters I am using are:<br>
constrained_magnetization = 'total direction'<br>
fixed_magnetization(3) = 0.0<br>
lambda = 0.2<br>
ecutwfc = 30.0 ,<br>
ecutrho = 300.0 ,<br>
occupations = 'smearing' ,<br>
degauss = 0.005,<br>
smearing = 'mv' ,<br>
nosym=.true.<br>
mixing_mode = 'local-TF' ,<br>
mixing_beta = 0.9 ,<br>
diagonalization = 'david' ,<br>
<br>
<br>
Which parameter on earth keep my calculations non-converged?<br>
<br>
<br>
Best,<br>
Yun-Peng<br>
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