[Pw_forum] Lowdin Charge- sign

Stefano de Gironcoli degironc at sissa.it
Sat Dec 11 10:29:12 CET 2010

In a pseudopotential calculation core electrons are not there so if you 
want to "see" the core electrons you need to do an all-electron 
calculation or a PAW calculation where the total  charge is reconstructed.
If you are interested in knowing a total atomic charge this is easy... 
just add to the valence electron charge the number of (completely 
filled) core electrons, change sign and add the nuclear charge..
notice however that the decomposition of a charge distribution in  
atomic contribution is a somewhat ill defined procedure and Lowdin 
procedure is just one possibility, so do not attach too much 
significance to minor changes from system to system...

Something that can be useful to identify bonding in your system can be 
the analysis of the projected density of states on atomic levels of 
nearest-neighbor atoms. It is sometime possible to see peaks occurring 
in the same energy range for the two atoms that signal that electronic 
states in that energy range are shared between the  two atoms as one 
expect in a covalent bond.

Hope it helps.

Stefano de Gironcoli

David Grifith wrote:
> Dear Heather
> Thanks for your comments. I think that this type of charge (Lowdin) which is
> nearly the number of valence electrons can not speak about the details of
> the system.
> Some electrons are bonding and also, the effect of the core (core electron +
> nucleus ) is not negligible. I want to compare the real charge of two atoms
> in my system with each other not their valence electrons. I appreciate your
> help in advance.
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