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<div class="moz-cite-prefix">Dear Pedro,<br>
in a solid, the polarization is defined modulo a lattice
translation (times e/cell_volume). See for instance
<a class="moz-txt-link-freetext" href="http://www.physics.rutgers.edu/~dhv/pubs/local_preprint/dv_fchap.pdf">http://www.physics.rutgers.edu/~dhv/pubs/local_preprint/dv_fchap.pdf</a><br>
You can understand this also by noticing that a complete basis set
is given by each WF translated by a generic real-space vector R;
the minimization routine in the code can pick up any of these.<br>
<br>
In your case of a single molecule and not of a solid, you should
try to translate all Wannier centres back inside the unit cell to
have a meaningful result (you may also try the translate_home_cell
input flag that should do this automatically).<br>
<br>
At this point you should get the same result. If you still get
slightly different results: it seems to me that the two
relaxations that you have done provide different atomic positions
for the H20 molecule (apart for the global shift).<br>
Try to simply do the h20.relax step once; then simply rigidly
translate the molecule to the cell centre, and perform a
scf+nscf+wannier calculation to check your results.<br>
<br>
Best,<br>
Giovanni Pizzi<br>
<br>
<br>
On 07/17/2012 08:07 PM, Pedro Augusto F. P. Moreira wrote:<br>
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<blockquote cite="mid:5005A9CE.60803@ifi.unicamp.br" type="cite">
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Dear all.<br>
<br>
I am trying to calculate electric dipole moments of an isolated
water molecule through Wannier functions (Wannier90 and QE).
Basically, I want to reproduce the results on Silvestrelli &
Parrinello, 1999 - J Chem Phys. Their computations were performed
at the Gamma point only of the Brillouin zone, with a plane-wave
cutoff of 70 Ry and a BLYP density functional. The monomer was
optimized in a cubic supercell of side 10.6 Å. They found a
dipole moment of 1.87 D.<br>
<br>
I used the same description in two simulations. However, in one
of them, the water molecule were translated by 5.0 Å at
z-direction in the beginning of the computations. That is the only
difference between the simulations. I provide the inputs and the
main results attached to the e-mail. My WF calculations followed
steps below:<br>
<br>
<big><small>1) pw.x < h2o.relax > relax.out<br>
</small></big><big><small>2) pw.x < h2o.nscf > nscf.out<br>
3) wannier90.x -pp h2o <br>
4) pw2wannier90.x < h2o.pw2wan > pw2wan.out <br>
5) wannier90.x h2o<br>
<br>
In the centered-molecule simulation, I found 1.8559 D, which
I can say this value agrees with the paper one. While, in the
translated-molecule simulation, I found 103.4 D.<br>
The difference is enormous for two very similar simulations.
I cannot explain so great difference due to a translation that
is lesser than the supercell side. <br>
<br>
I would be pleased if someone could confirm my results. The
attached files with the characters '_tr' are of the
translated-molecule simulation. <br>
<br>
Cheers,<br>
<br>
Pedro Moreira<br>
<br>
--------------------------------<br>
IFGW - Unicamp - Brazil<br>
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<br>
<br>
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<br>
<br>
<pre class="moz-signature" cols="72">--
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 319 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31159
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