[Pw_forum] comparing gaussian03 with pwscf

[Stefano de Gironcoli]

how to carve an atom from a molecule or a solid is a long standing 
problem with no clear solution basically due to the fact that it is an 
ill defined problem as .
however I  think that Bader  analysis, based on defining atomic volumes 
from topological properties of the charge density rather than just  
nearest-neighbhor interatomic distances, give results that are more 
consistent with chemical intuition.
I remember for instance that in GaAs a description based on Voronoy 
polyhedra would assign higher charge to Ga than to As just because the 
As is "fatter" than Ga and a fraction of the charge that one would 
visually assign to it was in the Ga territory...  An analysis based on
Bader decomposition was instead consistent with the expectation. 
Unfortunately Bader analysis is not presently implemented among QE 
post-processing tools.
Other options to try to assign charges to atoms are Lowdin population 
analysis (it however depends on the  choice of atomic functions used) or 
construction of maximally localized Wannier functions that would help 
splitting the charge density in contributions with well identified 
origin...   both these two schemes are available using QE and/or 
wannier90 code.

hope this helps,
stefano

Eduardo Ariel Menendez Proupin wrote:
> If there is doubt on the approximations for lantanides, I suggest to 
> make some tests with something more "classic", such as NaCl or MgO and 
> then compare PWSCF vs GAUSSIAN with complete basis sets.
>
> One question? What is the useful information provided by the knowledge 
> of the charge transfer? Can it be correlated to any measurable 
> property (reactivity, entropy, adsorcion enrgy, ....) or with any 
> measurable and difficult to calculate property?
>
> Some years ago I calculated and reported some charge transfer and said 
> something about the ionicity. To know better, I calculated the charge 
> transfer in NaCl. For this, I integrated the charge density in the 
> Voronoi cells of Na and Cl, using the self consisten charge density 
> and the superposition of atomic densities. The difference is the 
> charge transfer or, more precisely, the charge that crosses the 
> boundary of the Voronoi cells.
> To my surprise, the charge transfer in NaCl is 0.1 electron, and not 1 
> electron as the textbooks suggest. I also tested it with MgO (0.2 
> instead of 2). So, where is hidden  the truth of the ionic bond?
>
>  
>
> -- 
> Eduardo Menendez
> ------------------------------------------------------------------------
>
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