[Pw_forum] measuring covalent vs. ionic nature of Li bonding in LiC6

[Nicola Marzari]

Yaser Rehem wrote:

> Can anyone offer alternate method(s) by which I can assess the  
> relative covalent vs. ionic nature of Li bonding in this structure?


Dear Yaser,

one measure that I like is the Born effective charge - it's a real
physical quantity, and it tells you how an atom responds to an
electric field.

If the bonding is ionic, the atom will respond exactly as you
expect from its formal charge - if covalent it will be different.

This topic has been often discussed in the ferroelectrics literature,
due to the interested in the origin for the "giant" effective
charges of O.

You could also look at a recent PRB by Abdallah Qteish (Phys. Rev. B 75,
085201 (2007)) on ionicity.

			nicola

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