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

[Alvaro Vazquez Mayagoitia]

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

On Mon, Dec 12, 2011 at 5:25 PM, Ask Hjorth Larsen <askhl at fysik.dtu.dk> wrote:
> Hi Nick
>
>
> On Mon, 12 Dec 2011, Nichols A. Romero wrote:
>
>> Hi,
>>
>> Two related questions:
>> 1. We tried to converge a Ni atom in a box and tried every combination
>>  of parameters we could think of, but we never got it to converge.
>>  Can someone send me an input file that works for an isolated Ni atom?
>
>
> I don't know whether this is the same issue, but for an isolated Fe atom,
> consider the following:
>
> * With the electron configuration 4s^1 3d^7, the s eigenvalue is lower
>  than the d eigenvalue, so we have to move an electron from d to s
>
> * And yet, with 4s^2 3d^6, the s eigenvalue is greater than the d
>  eigenvalue.  So we have to move the electron back.
>
> These two considerations make it impossible to converge the calculation
> unless artificially fixing the occupations, or alternatively by increasing
> the Fermi temperature to allow partial occupations.  The latter solution
> will result in a minimum energy being obtained with s and d channels being
> degenerate.  This appears to be one of the weird properties of Kohn-Sham DFT
> with LDA/GGAs.  I observed this using the AtomPAW class (from
> gpaw.atom.atompaw.  Not the DFT code called AtomPAW).
>
>
>
>>
>> 2. Can the set-up generator created a set-up based on a spin-polarized
>>  configuration (instead of spin-paired)? I modified the default value
>>  of spinpol in aeatom.py (AllElectronAtom constructor), but it still
>>  didn't seem to work.
>>
>
> That hasn't been implemented.
>
> Best regards
> Ask