[Ifeffit] Modelling texture in Artemis

[Matt Newville]

Hi Kristine,


On Thu, Aug 16, 2018 at 10:28 AM Kirstine Dalgaard <kjd at inano.au.dk> wrote:

> (I am not sure this is the correct way to reply to this thread, hopefully
> it works)
>
>
> Dear Matt
>
>
> Thank you for your reply! The standard, which is highly textured, is
> NbSe2. The Nb K-edge was scanned.
>
> The structure consists of layers with Nb coordinated to 6 selenium atoms
> in a trigonal prismatic manner. Thus, the environment is not isotropic. The
> nearest Nb-neighbors are e.g. only in the plane of the layer.
>
> The preferred orientation is with the stacking-axis perpendicular to the
> pellet plane.
>
>
> I then assume that I do have an effect of the non-random orientation of
> bonds/paths relative to the X-ray polarization?
>
>
> On slide 28 in this presentation by Bruce Ravel
> http://xafs.org/Workshops/NSLS2002?action=AttachFile&do=get&target=Ravel.pdf it
> is stated that:
>
> "FEFF is capable of computing the effect of polarization directly. The
> polarized theory is easily used in analysis with polarized data".
>
>
> However, how do I implement this in my analysis? Is there maybe a written
> guide?
>
>
>
Like Bruce wrote, to account for the polarization of the beam relative to
your sample, you can specify the direction of polarization in the feff.inp
file.   That is done by adding  a line ike

   POLARIZATION  1 0 0

which will put the polarization vector along the X axis for the cluster of
atoms in that feff.inp file.  The feffNNNN.dat files calculated this way
will include the effect of polarization.

I'm not entirely sure I have you geometry correct, but I think you are
saying that the layers are perpendicular to the axis of your sample disk,
which sits at 45 degrees to the incident beam.  I think that means the
polarization vector would be along  (1 0 1) (that is, in the X-Z plane)
with Z beling the sample normal.   But I'm not sure what the orientation of
your structure is relative to the sample normal...

Hope that helps,

--Matt
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