[Pw_forum] RE : A question on atomic magnetic moments

[Prasenjit Ghosh]

A small suggestion, try changing the smearing type, instead of using
mp, try using m-v or even simple gaussian is fine for small clusters.
Also, you should check the value of the contribution to total energy
from smearing (printed in the output after your calculations have
converged).......ideally for small clusters as yours, this should be
zero. This tells you that your smearing is physically small enough so
that the spurious effect of broadening becomes negligible.

With regards,

Prasenjit

On 14 February 2011 10:20, Giovani Faccin <faccin.giovani at gmail.com> wrote:
> Dear Cyrille,
>
> First of all, thanks for the reply on my post.
>
> Following your suggestion, I've run a few calculations with lower degauss
> values. In particular, the ones reported on the message for Duy Le were made
> with a much smaller value ( 0.005 ) than the original 0.02 from the first
> message. Besides that, I've tried degauss values as low as 0.002 without any
> significant improvement on the final magnetization.
>
> I'm still wondering how do people find 6.00 so easily for the magnetization.
> I'm trying with 2 different DFT codes and no way I'm reaching those results,
> even though bulk/dimer equilibrium distances and force constants appear to
> be ok.
>
> Any other ideas, just tell me, I'll try it and report back on the list.
>
> Thanks again,
>
> Giovani
>
>
> 2011/2/13 BARRETEAU Cyrille <cyrille.barreteau at cea.fr>
>>
>> Dear Giovani
>> Try to decrease the degauss value of your smearing.. and see what happens.
>>
>>  cyrille
>>
>>
>> ==================================================================
>> Cyrille Barreteau
>>  phone : +33 (0)1 69 08 29 51
>> CEA Saclay                                                             fax
>> :      +33 (0)1 69 08 84 46
>> IRAMIS, SPCSI,    Batiment 462                            email
>> cyrille.barreteau at cea.fr
>> 91191 Gif sur Yvette Cedex
>> FRANCE
>> ~~~~~~~~~~~~~~~~~~~~~~~~
>> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
>> ==================================================================
>>
>> ________________________________
>>
>> De: pw_forum-bounces at pwscf.org de la part de Giovani Faccin
>> Date: dim. 13/02/2011 07:16
>> À: PWSCF Forum
>> Objet : Re: [Pw_forum] A question on atomic magnetic moments
>>
>>
>> Dear Paolo,
>>
>> Thanks for the reply.
>>
>> Just to make sure that the simulation cell size is not an issue (so that
>> the system is really finite), I've tested different possibilities, including
>> some quite big cells. Still, after a certain size the value of the
>> magnetization is converging to 6.82 instead of the expected 6.
>>
>> So something else is causing this. Unfortunately I've got no clue as to
>> what could it be.
>>
>> Should it be of any help, this is my input file:
>>
>>
>>  &CONTROL
>>                 calculation = 'scf' ,
>>                restart_mode = 'from_scratch' ,
>>                  wf_collect = .true. ,
>>                      outdir = './output' ,
>>                  pseudo_dir = '../pseudo/' ,
>>                      prefix = 'fe' ,
>>               etot_conv_thr = 1.0D-9 ,
>>               forc_conv_thr = 1.0D-6 ,
>>                     tstress = .true. ,
>>                     tprnfor = .true. ,
>>  /
>>  &SYSTEM
>>                       ibrav = 1,
>>                   celldm(1) = 43,
>>                         nat = 2,
>>                        ntyp = 1,
>>                     ecutwfc = 100 ,
>>                     ecutrho = 300 ,
>>                 occupations = 'smearing' ,
>>                     degauss = 0.02 ,
>>                    smearing = 'methfessel-paxton' ,
>>                       nspin = 2 ,
>>   starting_magnetization(1) = 1.0,
>>  /
>>  &ELECTRONS
>>                    conv_thr = 1.0e-9 ,
>>                 mixing_beta = 0.7 ,
>>             diagonalization = 'david' ,
>>  /
>> ATOMIC_SPECIES
>>   Fe   58.69000  Fe.pbe-nd-rrkjus.UPF
>> ATOMIC_POSITIONS angstrom
>>   Fe      0.000000000    0.000000000    0.000000000
>>   Fe      2.047510       0.000000000    0.000000000
>> K_POINTS automatic
>>  1 1 1   1 1 1
>>
>> Any suggestions are highly welcome.
>>
>> Giovani
>>
>>
>>
>> 2011/2/12 Paolo Giannozzi <giannozz at democritos.it>
>>
>>
>>
>>        On Feb 11, 2011, at 17:09 , Giovani Faccin wrote:
>>
>>        > My question: shouldn't those numbers be integers?
>>
>>
>>        only in finite systems, if you neglect spin-orbit.
>>
>>        P.
>>        ---
>>        Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
>>        Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>>        Phone +39-0432-558216, fax +39-0432-558222
>>
>>
>>
>>
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>>
>>
>>
>>
>> --
>> Giovani
>>
>>
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>
>
>
> --
> Giovani
>
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>



-- 
PRASENJIT GHOSH,
Assistant Professor,
IISER Pune,
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