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Dear Pietro, <br>
<br>
thank you for your help. I think that your description of what
happened is probably accurate, because the displacement of the
'fixed' atoms is a bit unexpected (actually, these atoms are fixed
so as to maintain a stress on a defect, and the stress field is
changing as a function of the defect moving. Therefore if the
'fixed' atoms were completely free, the stress field would
completely relax, which is not the case here.). The displacements
are compatible with those associated to the spring forces only. <br>
<br>
I will try to use the trick that you suggested. I am reasonably
confident it could address my issue.<br>
<br>
Thank you again, <br>
<br>
Best regards<br>
<br>
Laurent<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 24/10/2019 18:41, Pietro Delugas
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:f6ab83e7-52c2-6a8b-606c-a1c79a49e3c6@sissa.it">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<p><font size="-1">Dear Laurent <br>
</font></p>
<p><font size="-1">It might be that the fixed-position acts only
at the "engine" level inside pw, the forces are then are sent
to the path level and there the longitudinal component is
changed accordingly to the neb algorithm you are using, if
the neb part of the program is unaware of the fixed positions
then these atoms could be moved. When fixed positions are
equal for all the images this is not an issue as distances on
that coordinate are all zero and the longitudinal reaction
will also be 0. <br>
</font></p>
<p><font size="-1">I am just guessing though. I should look in the
code to see if this is what's actually happening. <br>
</font></p>
<p><font size="-1">In the meantime you could try set <br>
</font></p>
<p><font size="-1">use_masses = .true. in the &path namelist
and then specify fictitious masses, something like 1 for
atoms which are free to move and 10000 for the fixed ones. <br>
</font></p>
<p><font size="-1">hope it helps <br>
</font></p>
<p><font size="-1">regards - Pietro </font><br>
</p>
<div class="moz-cite-prefix">On 21/10/19 10:08, Laurent Pizzagalli
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:fc4bf9f5-9421-28ea-87de-9f58c4d2c967@univ-poitiers.fr">Dear
all, <br>
<br>
I encountered a weird and unexpected behavior when running a NEB
calculation with QE. In this calculation, several (boundary)
atoms are fixed. All initial images were provided in the input
file, with the required flags "1 1 1" for mobile and "0 0 0" for
fixed atoms. However, during NEB iterations, the positions of
the fixed atoms are updated with new values, which is obviously
something I'd like to avoid. It appears in all images, except in
the first one. <br>
I do not understand the issue, because in the 'PW.out' output
files contained in the subdirectories associated to each image,
one can clearly see that the '0 0 0' flags are correctly set for
the fixed atoms, for all images, and are conserved throughout
the calculations. Still, the coordinates of these atoms are
evolving. Moreover, in the .crd ouput file in the main
directory, which includes the updated coordinates for all images
during the NEB calculations, only the fixed atoms of the first
image have the '0 0 0' flags. <br>
<br>
One specificity of my calculation is that the (x,y,z) positions
of the fixed atoms change from one image to the other (but the
ordering of the atoms in each image is the same). This is not
common, and I was wondering whether this could be the cause of
my issue? If not, I do not have a clue why I got this weird
behavior. <br>
<br>
Any help or suggestions are welcome, <br>
<br>
Best regards <br>
<br>
L. Pizzagalli <br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
Quantum ESPRESSO is supported by MaX (<a class="moz-txt-link-abbreviated" href="http://www.max-centre.eu/quantum-espresso">www.max-centre.eu/quantum-espresso</a>)
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