[Pw_forum] NEB Image Continuity

[Vic Bermudez]

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