[gpaw-users] Ni in a box doesn't convergence and spin-polarized set-up

[Ask Hjorth Larsen]

Hi

On Tue, 13 Dec 2011, Alvaro Vazquez Mayagoitia wrote:

> Hi Ask,
>
> yes, Ni is a weird/tricky example, even for gaussian basis set codes
>
> I tried adding
>  fixmom=True
> and
>  occupations=FermiDirac(x)
> (with 0<x<1)
>
> and no success,
>
> Could you provide me an example, please?
>
>
> Thank you in advance,
> -Alvaro

Note that it isn't entirely trivial whether the calculation makes *sense* 
when the occupations are fractional - but I think it's the most correct 
way (given multiple "incorrect" alternatives) to deal with the problem.

This works:

from ase import Atoms
from gpaw import GPAW, FermiDirac, PoissonSolver

system = Atoms('Ni')
system.center(vacuum=5.0)
calc = GPAW(occupations=FermiDirac(0.3), hund=True,
             poissonsolver=PoissonSolver(relax='GS', eps=1e-8))

system.set_calculator(calc)
system.get_potential_energy()



(the Poisson solver just makes it take less time)

You can probably reduce the Fermi smearing (just tested that it works down 
to 0.1).

Regards
Ask