[Pw_forum] occupations from input

[Lorenzo Paulatto]

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/



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