[Wien] coordinate system for klist

[Gavin Abo]

I'm not an expert on crystal coordinate systems.

case.klist and case.klist_band need to use the same coordinate system, 
right?  Both seem to be read by inilpw.f when unit 4 is used in case.in1.

In the Wien2k 12.1 user guide for case.klist:

We use carthesian coordinates in units of 2pi/a, 2pi/b, 2pi/c for 
P,C,F and B cubic, tetragonal and orthorhombic lattices, but internal 
coordinates for H and monoclinic/triclinic lattices

carthesian - the "h" in the UG seems to be a typo

In SRC_kgen/birken.text:

USE of klist in inilpw.f of SRC_lapw1
-------------------------------------
...
 >>>>> orthogonal lattices
...
       << k-points in scaled cartesian coord. [2pi/a,2pi/b,2pi/c] >>

 >>>>> non-orthogonal lattices
...
       << k-points in fractional coordinates [b1,b2,b3] >>

As Ron mentioned, there is the if statement (SRC_lapw1/prtkpt.F) that 
converts the 'CONVENTIONAL reciprocal vectors' (of the b-centered cell) 
to the 'PRIMITIVE reciprocal vectors'.

This does seem to suggest that SRC_lapw1/inilpw.f reads 'CONVENTIONAL 
reciprocal vectors', or Conventional-ITA by Bilbao Crys. Server, for the 
C(monoclinic) lattice.

If the xcrysden output for C(monoclinic) needs to be CONVENTIONAL 
instead of PRIMITIVE, it should be easy to change in 
xcrysden-1.5.53/F/getintcoor.f.

On 10/29/2012 6:55 PM, Ronald Cohen wrote:
>
> On Mon, Oct 29, 2012 at 8:54 PM, Ron Cohen <rcohen at ciw.edu 
> <mailto:rcohen at ciw.edu>> wrote:
>
>     In xcrysden there is the following code:
>     c
>     ------------------------------------------------------------------------
>     c     **** **** WIENXX definition::
>     c
>     ------------------------------------------------------------------------
>     c     H, R, P, C(monoclinic) --> correspond to PRIMITIVE
>     reciprocal vectors
>     c                   ^^^^^^^^^^^^  is this really true !!!
>     c     F, B, C(orthorhombic)  --> correspond to CONVENTIONAL
>     reciprocal vectors
>
>     So it seems the issue of coordinate systems is indeed confusing.
>     What exactly are they? Thanks! Ron
>
>
>         On Mon, Oct 29, 2012 at 6:49 PM, Ronald Cohen
>         <cohen at gl.ciw.edu <mailto:cohen at gl.ciw.edu>> wrote:
>
>             I am trying to do band structures for C2/c and having
>             difficulty figuring out the coordinate system for
>             klist_bands . I had to modify my structure to B2/b because
>             wien2k doesn't allow normal monoclinic settings. But now I
>             have the issue of what are the coordinates in klist_bands.
>              I found this in lapw1:
>
>                   IF(.not.ORTHO.and.lattic(1:3).eq.'CXZ') then
>                    sxhelp=sx
>                      sx=sx+sz
>                    sz=-sxhelp+sz    ! fixed CXZ bug
>                   endif
>
>             So it seems only in this case is the coordinate system
>             changed.  It seems it should be the conventional primitive
>             lattice kpoints, so that 100 ( 40 0 0 40 for example)
>             would be a reciprocal lattice point. Or is it in the
>             centered reciprocal lattice? If the latter, is the
>             transformation printed anywhere?
>
>             xcrysden seems to generate in primitive coordinates, as
>             does aflow, so that would be convenient.
>
>             Thank you!
>
>             Sincerely,
>
>             Ron
>

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