[Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs

[peter]

Hi Cyrille,
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?

best,
Yun-Peng

On 09/12/2015 03:30 PM, BARRETEAU Cyrille wrote:
> Dear Yun-Peng,
>
> >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.
>
> Cyrille
>
>
> ========================
> *Cyrille Barreteau*
> CEA Saclay, IRAMIS, SPECBat. 771
> 91191 Gif sur Yvette Cedex, FRANCE
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> DTU Nanotech
> Ørsteds Plads, building 345E
> DK-2800 Kgs. Lyngby, DENMARK
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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> email: cyrille.barreteau at cea.fr /cyrbar at nanotech.dtu.dk
> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
> ========================
> ------------------------------------------------------------------------
> *De :* pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la 
> part de yuewen.fang [yuewen.fang at gmail.com]
> *Envoyé :* samedi 12 septembre 2015 20:42
> *À :* pw_forum
> *Objet :* Re: [Pw_forum] magnetic anisotropy calculation using 
> fully-relativistic PPs
>
> Hi, Yun-Peng,
>
> 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.
>
> Bests
> Fang
>
> ------------------------------------------------------------------------
>
> Yue-Wen FANG, PhD candidate
>
> East China Normal University <http://english.ecnu.edu.cn/>
>
>
> < peter <mailto:petercybertron at gmail.com>> 2015-09-13 02:16:28 wrote:
>
>     Thank you for your suggestions!
>     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).
>     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.
>
>     best,
>     Yun-Peng
>
>     On 09/11/2015 08:08 PM, yuewen.fang wrote:
>>     Dear Yun-Peng,
>>
>>     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.
>>
>>     Bests
>>     Fang
>>
>>     ------------------------------------------------------------------------
>>     Sent from YoMail <http://www.yomail.com/?utm_source=signature>
>>
>>     < Peter Cybertron <mailto:petercybertron at gmail.com>> 2015-09-12
>>     03:10:31 wrote:
>>
>>         Hi,
>>
>>
>>         I am working in University of Florida as a postdoc.
>>         I am exploring the spin-orbital calculations using pwscf, and I
>>         encounter a very slow convergence like this:
>>         > grep estimated scf.out
>>         estimated scf accuracy < 0.00000004 Ry
>>         ... (100 similar lines)
>>         estimated scf accuracy < 0.00000003 Ry
>>         > grep "total energy" scf.out
>>         ...
>>         total energy = -3667.91077719 Ry
>>         total energy = -3667.91078176 Ry
>>         total energy = -3667.91077642 Ry
>>         total energy = -3667.91078300 Ry
>>
>>
>>         Although the convergence of total energy seems OK (down to
>>         0.00001 Ry ~
>>         0.0001 eV = 0.1 meV), I still feel uncomfortable since I
>>         never encounter
>>         such a problem without spin-orbit interactions.
>>
>>
>>         I downloaded the ultrasoft and PAW pseudopotentials from
>>         PSLib and I am
>>         using the PBE flavor of XC functional. The system I am
>>         studying is a two
>>         dimensional magnetic insulator.
>>
>>
>>         The parameters I am using are:
>>         constrained_magnetization = 'total direction'
>>         fixed_magnetization(3) = 0.0
>>         lambda = 0.2
>>         ecutwfc = 30.0 ,
>>         ecutrho = 300.0 ,
>>         occupations = 'smearing' ,
>>         degauss = 0.005,
>>         smearing = 'mv' ,
>>         nosym=.true.
>>         mixing_mode = 'local-TF' ,
>>         mixing_beta = 0.9 ,
>>         diagonalization = 'david' ,
>>
>>
>>         Which parameter on earth keep my calculations non-converged?
>>
>>
>>         Best,
>>         Yun-Peng
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>>
>>
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