[Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs

[Ari P Seitsonen]

Dear Peter (or Yun-Peng??),

   Two wild guesses: 1) Did you check that the cut-off energies employed 
are sufficient? 2) The 'mixing_beta' is very large; the smaller this 
value, the tighter the convergence. Well, up to some limit; I would try a 
value closer to 0.3 or so. (If your system has a band gap, I do not know 
how the 'mv' broadening affects the occupation numbers.)

     Greetings from Paris,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Ecole Normale Supérieure (ENS), Département de Chimie, Paris
   Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Fri, 11 Sep 2015, Peter Cybertron 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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