[Pw_forum] scf calculation for isolated hydrogen atoms

[Gabriele Sclauzero]

Gabriele Sclauzero wrote:
> 
> Try for instance to run ld1.x with the following input:
>   &input
>      title='H'
>      prefix='H_',
>      zed=1,
>      config='1s1'
>      iswitch=1,
>      rel=0,
>      dft='PZ'
>      isic=1,
>   /
> 
> You get:
>       n l     nl                  e(Ry)          e(Ha)          e(eV)
>       1 0     1S 1( 1.00)        -1.0000        -0.5000       -13.6057
> 
> but if you use isic=0 you'll get:
> 
>       n l     nl                  e(Ry)          e(Ha)          e(eV)
>       1 0     1S 1( 1.00)        -0.4673        -0.2337        -6.3583
 >
 > which is much close to what you get from a pw.x LSDA calculation with fixed occupations in
 > a very big cell (around -7.3 eV). There is still a 1 eV difference that I cannot explain,
 > maybe it is due to something related to what you said.
 > Or maybe I am completely mistaken and there is some point I cannot get.

I understood what was missing here: I was comparing LSDA calculations of pw.x with 
non-spin-polarized calculations of ld1.x.

With the following input for ld1.x:

  &input
     title='H'
     prefix='H_',
     zed=1,
     config='1s1'
     iswitch=1,
     rel=1,
     lsd=1,
     dft='PZ'
     isic=0,
     latt=0,
  /

I got
      n l     nl                  e(Ry)          e(Ha)          e(eV)
      1 0     1S 1( 1.00)        -0.5383        -0.2691        -7.3239
      1 0     1S 2( 0.00)        -0.1666        -0.0833        -2.2673


while in the pw.x calculation I got:

  ------ SPIN UP ------------


           k = 0.0000 0.0000 0.0000 (136713 PWs)   bands (ev):

     -7.2894

  ------ SPIN DOWN ----------


           k = 0.0000 0.0000 0.0000 (136713 PWs)   bands (ev):

     -2.2862


So now the KS eigenvalues of pw.x and ld1.x calculations match within 0.05 eV.



HTH

GS

-- 


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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
|        via Beirut 2-4, 34014 Trieste (Italy)     |
| email: sclauzer at sissa.it                         |
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