[Pw_forum] scf calculation for isolated hydrogen atoms

[Gabriele Sclauzero]

Dear Dimpy,

Dimpy Sharma wrote:
> Hi there,
> I tried to calculate the ground state energy for isolated hydrogen atom 
> with the following input,however I got the fermi energy level at 
> -3.5661eV, while it should be -13.6eV.

I think that in your calculation, the Fermi level will be approximatively equal to the 1s 
electron energy level. You should be aware that you are using a pseudopotential code: even 
in the case of a one electron system you won't get something close to the true energy of 
the 1s level of the hydrogenoid atom unless you use an all-electron formalism (maybe PAW 
can give a n AE energy estimate).
Anyway, another big problem here is the self-interaction error. Even an AE calculation 
would give you a not so good value, I suspect.
Maybe you can get something close to the experimental energy level by using ld1.x (as Lihn
suggested) and enabling the self-interaction correction (see Doc/INPUT_LD1.txt).
Besides all this, I believe that in general it is better to use fixed occupations from 
input, rather than smearing, in atomic calculations with pw.x.

HTH

GS

> 
> &CONTROL.
>      calculation ='scf'
>     restart_mode = 'from_scratch'
>           outdir = '/sfiwork/dsharma/eigenvaluesSi/wf_H/'
>       pseudo_dir = '/sfiwork/dsharma/QE_Pseudos/'
>           prefix = 'H'
>          tstress = .true.
>          tprnfor = .true.
>         wf_collect =.true.
>  /
>  &SYSTEM
>         ibrav = 1
>     celldm(1) = 15
>           nat = 1
>          ntyp = 1
>       ecutwfc = 40
>       ecutrho = 160.0
>          nbnd = 2,
>          nspin=2,
>        starting_magnetization(1)=0.5
>     nosym=.true.,
>     occupations='smearing',
>     smearing='mp',
>     degauss=0.01,
> 
>  /
>  &ELECTRONS
>     diagonalization ='cg'
>         mixing_mode = 'local-TF'
>            conv_thr = 1.0d-6
>         mixing_beta = 0.7
> /
> ATOMIC_SPECIES
>    H   1.00794  H.pz-vbc.UPF
>   ATOMIC_POSITIONS angstroms
>     H   0.0000  0.0000 0.0000
> K_POINTS automatic
>  1 1 1   0 0 0
> 
> Thanks
> 
> Dimpy
> UCC
> Ireland
> 
> 
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| Gabriele Sclauzero, PhD Student                  |
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