[Pw_forum] occupations from input

[udayagiri sai babu]

dear Lorenzo PaulattoThank you for you clear explanation i understood it
now. previously i was not clear how these fractions are coming but now it is
clear. Thank you very much for your explanation

On Sat, Sep 12, 2009 at 1:45 PM, Lorenzo Paulatto <paulatto at sissa.it> wrote:

>
> On Sat, September 12, 2009 08:15, udayagiri sai babu wrote:
> >  Dear all
> >  Can somebody clearly tell me how to define occupations from input. I
> cant
> >  find much about that in this forum. The card "occupations" described in
> >  the
> >  example 11 for Al is not at all clear to me. What are those values mean.
> >  Looking forward to your help....
>
>
> It's quite easy, actually, there are only a couple of points you have to
> keep in mind:
>
> 1. if nspin=1 occupations can go from 0 to 2, you have to specify the
> occupation from the lower to the highest band and the sum of the
> occupations will have to be the number of electrons;
>
> 2. if nspin=2 occupations go from 0 to 1, you specify the occupation for
> spin up first, then for spin down (always on a newline);
>
> Let's say you want to reproduce the calculation of the Cr isolated atom,
> with semicore states in valence: 3s2 3p6 4s1 3d5 4p0
>
> first with nspin=1 and spherical (as it is done in ld1.x):
> OCCUPATIONS
>  2    2 2 2   1   1 1 1 1 1   0 0 0
> !3s2    3p6   4s1     3d5        4p0
>
> then spin polarized (nspin=2), according to Hund's rule you have to
> maximize the total angular momentum:
> OCCUPATIONS
>  1    1 1 1   1   1 1 1 1 1   0 0 0
>  1    1 1 1   0   0 0 0 0 0   0 0 0
> !3s2    3p6   4s1     3d5        4p0
>
> Chrome is a lucky case, as it has a spherical ground state. As a last
> example let's take an oxygen atom (2s2 2p4) and set the occupations to
> reproduce the ld1.x calculation:
> OCCUPATIONS
>  2  4/3 4/3 4/3
>
> or, equivalently:
> OCCUPATIONS
>  2    1.333333 1.333333 1.333334
>
>
> I hope it helps, best regards
>
> --
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/<http://people.sissa.it/%7Epaulatto/>
>
>
>
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-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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