dummy questions about Bader charges

[kambiz]

Hi,
Dear all

I have some dummy questions about Bader charges and I apologize if my questions are somehow very basic.

I have a CoO slab optimized suing PBE + U (spin polarized) . The final Bader charges for all Co atoms are ~ +1.24 and for O are ~ -1.24.

1. Should n't the charges of atoms at the first layer (surface) differ from those in the bottom layers?

2. After adsorption of a molecule on different positions, I can calculate the net charge transfer. For one case the net charge transfer is 0.50 e while for another one is 0.40 e. Is there a definition that I can say that the net charge transfer of 0.50 e is much bigger than that of 0.4 e?

3. Based on Bader charges, when can we say there is an ionic bond or a covalnet bond or other types of bonds?

Regards

[graeme]

We basically use the Bader charges as a relative measure of how charge is distributed. In terms of interpretation, deciding what is ionic or covalent, or how much charge transfer is significant, you are pretty much on your own.