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
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_______________________________________________
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
