Dear Pietro,
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.
I will try to use the trick that you suggested. I am reasonably
confident it could address my issue.
Thank you again,
Best regards
Laurent
On 24/10/2019 18:41, Pietro Delugas wrote:
Dear Laurent
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.
I am just guessing though. I should look in the code to see if this
is what's actually happening.
In the meantime you could try set
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.
hope it helps
regards - Pietro
On 21/10/19 10:08, Laurent Pizzagalli wrote:
Dear all,
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.
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.
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.
Any help or suggestions are welcome,
Best regards
L. Pizzagalli
_______________________________________________
Quantum ESPRESSO is supported by MaX
(www.max-centre.eu/quantum-espresso)
users mailing list [email protected]
https://lists.quantum-espresso.org/mailman/listinfo/users
_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
users mailing list [email protected]
https://lists.quantum-espresso.org/mailman/listinfo/users
--
,,, __,
/'^'\ |__|
( o o ) |
--------------------------------------------------oOOO--(_)--OO|o------
<[email protected]>
http://laurent.pizzagalli.free.fr/ Tel +33 549 49 74 99
------------------------------------------ Fax +33 549 49 66 92
Institut P'
Departement de Physique et de Mécanique des Matériaux
CNRS UPR 3346
Université de Poitiers
SP2MI
TSA 41123 .oooO
86073 Poitiers Cedex 9, FRANCE ( ) Oooo.
----------------------------------------------------\ (----( )-------
\_) ) /
(_/
_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
users mailing list [email protected]
https://lists.quantum-espresso.org/mailman/listinfo/users
