[Pw_forum] (no subject) (actually TOTAL ENERGY OF Na ATOM)

[Giovanni Cantele]

Hi,

first of all a little note: unless my e-mail server is going crazy, I think it is the sixth e-mail on the same topic sent in two or three days. This is a forum, where people voluntarily share their (little or big) knowledge and experience
with others. As such, once a question is made, it would be kind (this is my opinion, of course!) to wait for someone that, after reading the message, finds some time to spent to provide an answer. Posting multiple messages,
usually delays the answer!!!   

Moreover, I think it is quite inefficient to post messages with no subject, since this does not allow to immediately identify which reply concerns a given thread.

This being said, this is what I could notice as far as your question is concerned:

1) your original question, that is, “is -92.306…… Ry” the energy of an Na atom?, is not really well posed, since the total energy depends on cutoff, pseudo potential, and so on, so just the value
of the total energy might be meaningless, much better to share input file (as you did later) to understand how such an energy is calculated

2) if you need such energy to calculate the adsorption energy, you should decide if your reference is an hypothetic gas of Na atoms or bulk Na, in the latter case you should calculate the total
energy per Na atom of bulk Na, instead

3) you are using an ultra soft pseudo potential, that means that the default value of ecutrho=4*ecutwfc might be insufficient or, in some cases, even provide truly wrong results. As such, you should check
the convergence also with respect to ecutrho, in any run where ultra soft pseudos are involved. Consider that even the cutoff is maybe too small. In the pseudo file you’re using, you should find two lines
like:
    Suggested minimum cutoff for wavefunctions:  66. Ry
    Suggested minimum cutoff for charge density: 323. Ry
So 35 Ry, in comparison, looks really small!

4) as already suggested, If the total energy of an isolated Na atom is exactly what you need, you should also look for a spin polarised ground state, to check if including the spin degree of freedom leads
to a lower energy ground state

5) again, If the total energy of an isolated Na atom is exactly what you need, your unit cell is likely to be too small, only 4 A separate two neighbour periodic replicas of the Na atom, an this is not enough
to ensure no interaction between the periodic replicas

6) again, If the total energy of an isolated Na atom is exactly what you need, you don’t have to sample the Brillouin zone with an 8x8x1 grid, because if the atom is truly isolated (see previous point),
the energy levels are flat, so just gamma point is enough



Giovanni

> On 15 Jun 2017, at 17:03, nipesh dulal <nipeshdulal25 at gmail.com> wrote:
> 
> Hello Everyone 
> 
> I have calculated the ground state energy of Sodium Atom. The final result is -92.3063689424Ry. I have use below input file. Is it correct?
> 
>  &control
>     calculation='relax',
>     verbosity='high'
>     prefix='sodiumrelax'
>     outdir='/home/quantumespresso/Downloads/graphene/adsorption'
>     pseudo_dir = '/home/quantumespresso/Downloads/graphene/pseudopotentials',
>     tprnfor=.true.
>     forc_conv_thr=1.0d-3
>     tstress=.true.
>     etot_conv_thr=1.0d-4 
>     
>     
>  /
>  &SYSTEM
>  ibrav=3
>  celldm(1)=8.906
>  nat=1
>  ntyp=1
>  ecutwfc=35
>  occupations='smearing'
>  smearing='mv'
>  nbnd =12
>  degauss=0.002
>  /
>  &ELECTRONS
>  electron_maxstep = 100
>  mixing_beta=0.6
>  conv_thr = 1.0D-8
>  /
>  &ions
>  /
>  ATOMIC_SPECIES
>  Na 23.0 Na.pbe-spn-rrkjus_psl.0.2.UPF
> ATOMIC_POSITIONS (angstrom)
>  Na 0.000000000 0.000000000 0.0000000
>  
>  K_POINTS {automatic}
>  8 8 1 0 0 0
> 
> 
> With Best Regards
> NIpesh Dulal 
> Kathmandu,Nepal
> Trihbhuwan university 
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.fisica.unina.it/~cantele

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