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From: <rei...@fa...> - 2016-05-27 13:13:31
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Hi Kris,
Let me answer your questions:
*Neutron scattering wavelength:*
IN DISCUS I set the neutron scattering length in the Fourier menu. The
PDF menu does not offer a modification.
read
cell nickel.cell
#
fourier
neutron ! switch to neutron scattering
exit
show scat, all ! Show current scattering length
four
scat ni, 0,0, 0,0, 0,0, 0,0, 10.05 ! modify
! even though its a neutron scattering length
! one needs to set a(i), b(i), c as for X-ray...
exit
show scat, all ! Show modified scattering length
*Scaling experimental data:*
See the attached demo macro, which creates a Nickel PDF and
then modifies the Nickel structure, scale factor and refines
to match the "experimental data"
I realised that the on-line help is missing the info on the
"set refine" command within the PDF menu... To be corrected.
Best
Reinhard Neder
----------------------------------- Original Message -----------------------------------
Subject: [Discus-talk] Setting variables in DISCUS PDF module
From: "Kris Harris" <kri...@mc...>
Date: Thu, May 26, 2016 22:10
To: dis...@li...
----------------------------------------------------------------------------------------
Hi,
As a first exercise, I'm attempting to reproduce an RMC fit of a neutron
PDF from a published article. I've gotten close but don't know how to
change two parameters:
*Neutron scattering wavelength:* How do I read out (and change if needed)
these values? The command "show" produces a section called "Weights for
pdf calculations", but I don't see how to connect this to values of b_i in
the equation given in the manual for G(r).
*Scaling experimental data:* My initial simulations look close, but I need
to scale the entire simulation smaller to about 80% to match the
experimental data. I'm guessing it's theoretically OK to do this? The
manual lists a variable pdf_scal[i] but I can't seem to figure out the
syntax to set it. I guess scaling the value of the average scattering
power, <b>, would do the same thing, but I'm not sure how to do that either.
thanks for any help,
Kris
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Prof. Dr. Reinhard Neder
Kristallographie und Strukturphysik
Universität Erlangen
Staudtststr. 3; 91058 Erlangen
tel. +49-9131-8525191
fax +49-9131-8525182 |