[Pw_forum] Request about the "real" total energy

[Nicola Marzari]

Dear Steve,

Indeed, you are freezing the core electrons in a pseudopotential - if 
atomic energies are
what you are interested in, use the ld1.x code.

Of course, plane waves are not really the best choice for Hartree Fock 
calculations (use a
quantum chemistry codes) but if you are concerned about comparisons, 
maybe you could look
at potential energy surfaces - e.g. the dissociation of a molecule, or 
the frequency normal modes -
there you could compare Hartree-Fock within pw.x with other known results.

Still, there could be better choices to get acqainted with the code - 
maybe browse, from the
q-e website, the lectures/videos/tutorials of the 2009 Santa Barbara school.

       nicola


steve ndengué wrote:
> Dear all,
>
> We have an enquiry about some results appearing in the output file of 
> the pw.x run.
>
> We are trying to perform computations on isolated atoms to try to get 
> a significance of the results given by the code. We have to recall 
> that we are new users of QE. And as far as we know it is not too much 
> indicated for such kind of computations but it is rather a first try 
> to get some understanding on the "behaviour" of the code.
>
> So the problem is that when performing the computations on He for 
> example we obtain the correct ground state energy up to the 
> Hartree-Fock limit. But when applied to other atoms (Li, Na, Be, C, 
> ...) the value obtained do not correspond at all to the known value.
>
> We thus have 2 questions:
>
> 1- Why is it that the level of refinement obtained is the Hartree-Fock 
> limit; we may have expected a better accuracy? Is it linked to the use 
> of pseudo-potentials?
> 2- What can we do to recover the correct (up to the Hartree-Fock limit 
> at least) total energy for the other atoms?
>  
> Sincerely Yours,
> On behalf of the
> Groupe  de Structure et Dynamique des Atomes et Molecules
> Laboratoire de Physique Fondamentale
> Département de Physique
> Université de Douala.
>


-- 
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Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu