[Wannier] electric polarization of a single molecule
Pedro Augusto F. P. Moreira
pmoreira at ifi.unicamp.br
Wed Jun 6 20:15:16 CEST 2012
Dear all,
I am trying to calculate the electric polarization of an isolated
water molecule as Silvestrelli and Parrinello did in 1999 (PRL).
I did a molecule relaxation with QE and calculated the electric
polarization, using Wannier functions centres (from W90) and ions
positions. I considered my initial and final states, the initial and
final conditions on relaxation. However, I found a different value from
expected one.
Prof. Nicola Marzari answered before in this list:
http://www.democritos.it/pipermail/wannier/2009-January.txt
"Short answer: you can consider the center of each Wannier function as a
"classical" electron. So, the vectorial sum of all the Wannier centers
gives you an overall electronic polarization vector (you need to
multiply it by 2, if spin unpolarized, then by the charge of one
electron, and divide it by the volume of the unit cell). The
*difference* in this polarization vector between two phases (e.g. cubic
and tetragonal) gives you the *physical* quantity that you want (you
also need to add the same, trivial, for the ionic valence charges, to
have the total polarization difference)."
My question is: How should I choice two "phases" for a single molecule?
In other words: I know the formula for calculating the electric
polarization, but I do not know how to determine the initial and final
states to do the math.
Any advice would be appreciated,
Pedro
-----------------------------
Pedro Moreira
IFGW - Unicamp - Brazil
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