[Pw_forum] NEB Image Continuity

Paolo Giannozzi p.giannozzi at gmail.com
Tue Jan 26 12:09:42 CET 2016

A simple check that your path is what you expect and not something else is
provided by the "path length", a quantity that is reprinted on output. All
visualizers occasionally show atoms that seem to "jump" from one side to
the other of the cell.


On Sat, Jan 23, 2016 at 3:44 PM, Vic Bermudez <c.h.bermudez at cox.net> wrote:

> Hello,
>         I have a question about the issue of image continuity in NEB
> calculations.
> The NEB users' guide (vers. 5.0) contains the following cautionary note:
>         "Remember that Quantum ESPRESSO assumes continuity between the
> first and
> the last image at the initial condition. In other words, periodic images
> are
> NOT used; you may have to manually translate an atom by one or more unit
> cell base vectors in order to have a meaningful initial path."
> I've checked my reaction path by viewing the .axsf output file in XCrysDen
> with the setting Display -> Unit of Repetition -> Translational Asymmetric
> Unit. I don't see any problem with atoms jumping by one unit-cell vector
> between images or with atoms getting too close. I do, however, see a few
> atoms jumping when I use Display -> Unit of Repetition -> Unit Cell.
>         My understanding is that Quantum Espresso works with the
> Asymmetric Unit
> (or primitive unit cell), so my NEB path appears to satisfy the cautionary
> note. Is that correct ? Unfortunately, for technical reasons, I don't have
> access to vers. 5.1, so I can't simply use the minimum_image option that's
> available in vers. 5.1.
>         Thank you in advance for your help and advice.
> Best Wishes,
> Vic Bermudez
> Victor M. Bermudez
> E-mail: bermudez at alum.mit.edu
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Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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