[Wannier] Polarization of isolated H20 (dipole moment)
Pedro Augusto F. P. Moreira
pmoreira at ifi.unicamp.br
Fri Jun 29 23:06:14 CEST 2012
Dear all.
I am trying to calculate the spontaneous electric polarization of a
single water molecule as a test.
I am using Quantum Espresso (pw.x and wannier90). I did by two
methods: (1) using tefield=.true. as suggested by Cantele
(http://www.democritos.it/pipermail/pw_forum/2009-March/011936.html) and
(2) by Wannier function centres (WF).
I run a set of simulations with different initial atomic positions.
The first simulation, I used the positions mentioned by Cantele and
found P = 1.82 D and P =1.84 D by method (1). By WF, P= 1.90 D and 1.92
D. The first values are calculated with BLYP functional and the second
ones with PBE functional.
After that, I moved initially all atoms by a vector (1.0 0.0 0.0)
angstrom, relaxed the molecule and did again the calculations above. I
found for Cantele way: P = 1.78 D and 1.80 D. By WF, P = 6.33 D and 6.37 D.
My questions are:
(a) I expected to find values closer to 1.87 D in all calculations,
but all they are diverging from this value by, at least, 2 %. Should I
really expect it ?
(b) Anyone knows what can be happening in WF calculations when I moved
the atoms? I know that if the atoms were moved beyond the unit cell, a
constant factor would be summed to polarization. But, I think that is
not my case because the dislocation vector was 1.0 A , while my cubic
cell has 10.6 A edges.
With best regards,
Pedro
--
Pedro Moreira
IFGW - Unicamp - Brazil
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