[Pw_forum] neb.x with v5.0.2

Gabriele Sclauzero gabriele.sclauzero at epfl.ch
Wed Jun 5 17:15:46 CEST 2013

Dear Luca,

   thanks for reporting this problem. You still have two CO molecules in the final image, but the problem is that the interpolation between the initial and final images does not produce the path you wanted. The path generator assumes that an atom will not move by more than half a lattice vector between two consecutive images given on input (just two in your case, the initial and final ones). 
This is almost always the case, because one usually choses a supercell which is big enough to avoid spurious interactions between periodic replicas. In your case the cell is quite small and one oxygen moves by 0.56*alat along the x direction.
I see three possible solutions that do not require modifications of the code:
1. Use a larger supercell (e.g. 3x3 Rh(111), instead of 2x2)
2. Insert an intermediate image between the initial and final ones
3. displace slightly the CO_2 to the right in the initial image



> Yes, they are equivalent by a lattice translation but intermediate images are not equivalent, because they are set between the first image and a last image, different from the one I selected. I get “strange” structures of the intermediate images. I still have 2 CO molecules, but one is in my supercell, and the other is splitted, the C atom is in the supercell I built and the O atom is in the next one.
>  I also tried to run the same input file with version 5.0.1 and QE 5.0.1 kept all the atomic positions I listed in my input file.
> Thanks a lot,
> Luca Dietz
> Bachelor of Science in Chemical Engineering
> Politecnico di Milano, Italy

§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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