[Wien] Wavefunctions out of IBZ

[Fred Nastos]

On May 6, 2004 12:58 pm, Chiung-Yuan Lin wrote:
> Dear all,
>   I have a basic question here:
> How can I obain a wavefunction if its k lies out of IBZ (still in BZ)?
> I know how to get wavefunctions in IBZ. The k points out of IBZ are
> generated by symmetry operations. I think a non-IBZ wavefuntion is
> related to its corresponding IBZ wavefuntion in some way.

There are two straight-forward ways I can think of.

1) Change the klist file and include the k-point you want.
If you have allready run an scf cycle then lapw1 will then
generate the wavefunction at the specified k-point.  I use
my own k-meshes for BZ integrations, and this works great.
This is analogous to a bandstructure plot, 

2) If you look at the source code of kgen you will see how
k-points are "mapped" back to the IBZ.  By modifying the
source code you can track which k-point comes from where
and apply the correct symmetry relations.

Which method you pursue depends on the problem.  If you
are interested in a certain matrix element usually the matrix
element satisfies simple transformations (dpeending on
whether it transforms like a vector or pseudovector) so the
IBZ results are sufficient.

The following is just speculation:  I think one thing you don't
want to do is to interpolate the wavefunction between some
k-points.  Each state |nk> that comes from a diagonalization
routine can have an arbitrary phase attached to it, and this
may be difficult to deal with.