[Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs

[BARRETEAU Cyrille]

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, SPEC Bat. 771
91191 Gif sur Yvette Cedex, FRANCE
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DTU Nanotech
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email:     cyrille.barreteau at cea.fr  /cyrbar at nanotech.dtu.dk
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________________________________
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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