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Eyvaz Isaev wrote:
<blockquote cite="mid20060407150924.61726.qmail@web60325.mail.yahoo.com"
type="cite">
<pre wrap="">Dear Paolo,
--- Paolo Giannozzi <a class="moz-txt-link-rfc2396E" href="mailto:giannozz@nest.sns.it"><giannozz@nest.sns.it></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">this may actually work, but the problem that shows
up in Liping's output is rather strange and nasty.
</pre>
</blockquote>
<pre wrap=""><!---->
</pre>
<blockquote type="cite">
<pre wrap="">The self-consistent procedure seems to converge
quite nicely: |ddv_scf|^2 goes down towards the
threshold, then it starts to go up to crazy
values.
</pre>
</blockquote>
<pre wrap=""><!---->Yes, I paid attention to this behaviour. Actually,
recently I had very close situation: for some modes
everything was OK, and next mode also started well,
and then turned out to be crazy. At least in my case,
using small mixing parameter fixed the problem.
I suggest, Liping should keep us informed about the
problem.</pre>
</blockquote>
The same phenomenon still campe up in the self consistent<br>
calculation of representation # 6 if I only reduce aplpha_mix(1)<br>
to 0.1 and keep tr2_ph = 1.0e-18. So only using smaller mixing <br>
parameter doesn't work in this case. <br>
<br>
However it works as we expected if I set alpha_mix(1) = 0.1 <br>
and tr2_ph = 1.e-10. But the results (here 20-atom 2*2*1 supercell
used) <br>
don't agree well with those of calculation where 1*1*1 cubic perovskite
<br>
unit cell (5 atoms inside) are used. For example, the dielectric
constant of <br>
Srtio3, is for 2*2*1 supercell<br>
<br>
( 222.139158023 0.000000000 0.000000000 )<br>
( 0.000000000 222.139158023 0.000000000 )<br>
( 0.000000000 0.000000000 6.262166130 )<br>
and for 1*1*1 unit cell<br>
( 6.296436141 0.000000000 0.000000000 )<br>
( 0.000000000 6.296436141 0.000000000 )<br>
( 0.000000000 0.000000000 6.296436141 ).<br>
<br>
In direction of xx and yy, dielectric constants in two cases should be
pretty<br>
close to each other like the one in zz direction. I am not sure if the
problem<br>
comes from something related to the supercell I used. There is no such
problem<br>
for 1*1*1 unit cell when setting alpha_mix(1) = 0.7 and tr2_ph =
1.e-18. <br>
On the other hand, I am also wondering if it's also possible due to<br>
pseudopotential. Because there is no such problem for PbTiO3 in 2*2*1
supercell.<br>
Thanks for your comments!<br>
liping<br>
<br>
<blockquote cite="mid20060407150924.61726.qmail@web60325.mail.yahoo.com"
type="cite">
<pre wrap="">Bests,
Eyvaz.
</pre>
</blockquote>
<blockquote cite="mid20060407150924.61726.qmail@web60325.mail.yahoo.com"
type="cite">
<blockquote type="cite">
<pre wrap="">Why, I don't know, and I am afraid there is
very little one can do when this kind of behavior
occurs in the middle of a long job without any
apparent reason
</pre>
</blockquote>
<pre wrap=""><!---->
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</pre>
</blockquote>
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