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Re: [lammps-users] Using compute/xrd with manual c
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Re: [lammps-users] Using compute/xrd with manual c


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 6 Nov 2017 10:20:38 -0500

since this compute is part of a user package, your best chances to get help beyond what is documented in the manual, is to contact the (corresponding) author listed is the respective README file. not all authors of LAMMPS packages monitor the LAMMPS mailing list regularly.

axel.

On Mon, Nov 6, 2017 at 9:52 AM, Sebastian Hütter <sebastian.huetter@...7220...> wrote:
Hi all,

I want to use the xrd compute to obtain XRD powder patterns from a structure. As a simple test, I used bcc-Mo and the following input script: <https://gist.github.com/martok/9102b3e174e960e2f8a0be1fd8c7e3c4>

In general, this works well - but only for the "default" K-space lattice with c=1 1 1:
<http://puu.sh/yg4mv/758f9eda76.png>

Changing to a coarser lattice by increasing c>1 causes some peaks to be "missed" by the sampling - this is to be expected. Changing c<1 however completely destroys the result, effectively creating fake reflections at almost every K-space lattice point sampled:
<http://puu.sh/yg4n1/23f84d512b.png>

It is my understanding (which may be lacking...), that sampling points corresponding to angles of incidence that do not cause constructive interference should just cancel out (i.e. sum up to 0 in the final binning), so the final result should always be consistent?

The main consequence of this issue is that using a manual K-space lattice to compare different results is simply impossible, but the documentation clearly states that this should work, for example writing something like "c 0.05 0.05 0.05 manual".

Am I doing something wrong (probably) and if so, what?


Kind regards,

Sebastian

--
M.Sc. Sebastian Hütter
Otto-von-Guericke University Magdeburg
Institute of Materials and Joining Technology
Universitätsplatz 2
D-39106 Magdeburg
Tel.: +49 (0)391-67-54566
Fax: +49 (0)391-67-44569

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--
Dr. Axel Kohlmeyer  akohlmey@...92......  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.