[Wannier] Neighbour not found !

Giovanni Pizzi giovanni.pizzi at epfl.ch
Sat Dec 21 17:35:24 CET 2013

the .mmn file contains the M_{m,n}^{k,k+b} matrices, where {k,k+b} must be two first-neighbour points in your Monkhorst-Pack k-mesh.

In particular, if you go in the source folder of Wannier90 and do a
grep 'Neighbour not found' *.F90
you discover that the error is issued on the overlap.F90 file, and if you go in the file you also discover what the numbers printed in the line above mean:

count = 3 -> problem in the third block within the seedname.mmn file
nkp   = 1 -> "k" is the first k point in the list of kpoints in the nnkpts file
nkp2  = 6, nnl=nnm=nnn=0 -> "k+b" is the sixth point in the list, without any translation of a reciprocal lattice vector
nn    = 0 -> no nearest neighbor found

This means that the .mmn file has a M_{mn}^{k,k+b} matrix and it claims that "k"=1st point of the list, "k+b" = 6th point of the list, but actually this pair of (k,k+b) are not a pair of first neighbor k-points for your k-point list.

Unless you copied some of the output files generated by VASP and not all of them, mixing files of two different calculations, this seems to be a possible bug of the VASP interface, especially since this appears only with SOC. Double check, and then try to contact the VASP developers to get further help (they will probably need also your k-point list from the nnkp file, I guess).

Giovanni Pizzi

Giovanni Pizzi
Post-doctoral Research Scientist
MXC 340 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31124

On 21 Dec 2013, at 07:58, dwz wrote:

Dear Wannier experts :
When wannier90 reads the  overlap matrix file wannier90.mmn file  on my machine , it reports the following info :

- -Reading overlaps from wannier90.mmn    : File generated by VASP: MnCH
- -Error reading wannier90.mmn:       3    1    6   0    0  0  0
- -Exiting.......
- -Neighbour not found

What "neighbour not found " means ? What I can do to avoid such bug ?
 FYI : the mmn file is written when the SOC turned on. If the SOC switched off, the following procedure reports no bugs. I do not know whether this bug is induced by SOC, seemingly they are irrelevant.

Tom Dong
Shandong University , China .

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