[Pw_forum] scf calculation for isolated hydrogen atoms

[Gabriele Sclauzero]

Sorry, in my previous e-mail I have mistaken the concept. Actually pseudopotentials are 
built to fit to a good approximation the all-electron energy levels of the valence 
electrons. What would be different is the total energy of the system.
Anyway, the problem of self-interaction will remain, and I doubt that you could get 
exactly 1 Ry.

GS

Gabriele Sclauzero wrote:
> 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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> 

-- 


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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
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