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I don't know how to explain.. but when things are exactly zero it's
because there is a symmetry reason.<br>
like a mirror plane or something ...<br>
If your symmetry allows the born effective charge to be non zero
they will, much or little depending on the details of the system.<br>
<br>
Are the symmetry operations determined in the two systems the same ?<br>
<br>
stefano <br>
<br>
On 04/08/2011 10:19 AM, sonu kumar wrote:
<blockquote
cite="mid:BANLkTinOfHHrmJ2zXNtOY=-AvThgvS-ZDg@mail.gmail.com"
type="cite">
<pre wrap="">Sorry for my incomplete mail.
Dear Prof. Stefano de Gironcoli and QE users,
So one would expect to have anisotropic born charges with off-diagonal
elements for unit cell with R-3m space group.
However, in PHYSICAL REVIEW B 73, 155114 ͑2006͒ , NaHF2 have zero values
for off-diagonal
elements of born-charges and diagonal elements are:
H F Na
xx/yy .337 ~ -.7 1.057
zz ~2 ~ -1.5 ~1
Similary in CuAlO2 with same space group, i have found zero values of
off-diagonal elements of born tensor.
How you explain this?
With kind regards,
Sonu Kumar
IITD
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