On Thu, Aug 24, 2017 at 12:43:45AM +0100, Abderrahmane Reggad wrote:
> The reason for my question is that I don't how does a DFT code work and I
> want to know if the ionic state is a result or an assumption.


In a wien2k calculation you provide the number of electrons assigned
to the core and to the valence regions of each chemical species in your
system.  However that is defining a population in orbital space. If the
calculations proceeds appropiatelryi (convergence of results, convergence
o basis set [k space], etc). The final distribution of the electrons
should not be determined by your assumptions, so obtaining an ionic,
covalent, metallic, magnetic, etc result should be a consecuence and
not an assumption. However, you must examine the correctness of the
calculation performing the analysis that is described in wien2k user
guide (muffin tin radius, k vectors, ...)

The analysis of the wien2k wavefunction and density can produce the
approximate picture of a very ionic system (NaCl and MgO, for instance),
a mostly covalent crystal (diamond and graphite, for instance), a
metallic one (alkali metals), and so on.

You can check all those examples in (sorry to describe my own
publications, but those are things that I know quite well ;-) )

* Ions in crystals: The topology of the electron density in ionic
  materials. II. The cubic alkali halide perovskites
  V Luaña, A Costales, AM Pendás
  Physical Review B 55 (7), 4285

* A classification of covalent, ionic, and metallic solids based on
  the electron density
  P Mori-Sánchez, AM Pendás, V Luaña
  Journal of the American Chemical Society 124 (49), 14721-14723

* Non-nuclear maxima of the electron density on alkaline metals
  V Luaña, P Mori-Sánchez, A Costales, MA Blanco, AM Pendás
  The Journal of chemical physics 119 (12), 6341-6350

* Topological characterization of the electron density laplacian in
  crystals. The case of the group IV elements
  A Otero-de-la-Roza, V Luaña
  Journal of Chemical Theory and Computation 6 (12), 3761-3779

* Ions in Crystals: The Topology of the Electron Density in Ionic
  Materials. 4. The Danburite (CaB2Si2O8) Case and the Occurrence of
  Oxide− Oxide Bond Paths in Crystals
  V Luana, A Costales, P Mori-Sanchez, AM Pendás
  The Journal of Physical Chemistry B 107 (21), 4912-4921

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