[Ifeffit] FEFF calculation on ferri-/ferrocyanide materials

Matt Newville newville at cars.uchicago.edu
Sun Jan 23 12:50:54 CST 2022


Hi Yang,


On Sun, Jan 23, 2022 at 11:30 AM Hu, Yang (HIU) <yang.hu at kit.edu> wrote:

> Dear IFEFFIT members,
>
>
>
> I am trying to apply the FEFF calculation on Metal-[Fe(CN)6] type
> materials (in Larch). The calculations were successful with cif files from
> (K, Na)x(Cu, Ni) [Fe(CN)6]  for both C-coordinated Fe and N-coordinated
> metals, and their results include higher-order paths.
>
>
>
> However, the calculation on NaxFe[Fe(CN)6] always gives the warning “…Two
> atoms very close together. Check input…” and takes long time. The
> calculated results have some collinear 5- and 6-leg paths with several
> hundred or even thousand importance value.
>
>
>
> I am wondering if it is possible to limit the multiple scattering to a
> lower order in the calculation (such as suggested in Artemis user guide).
>
> Plus, if I only aim to model the nearest Fe-C and Fe-N for its Fe K-edge
> spectra, are there any alternative methods for the calculation? — I also
> would like to ask whether it is meaningful to do this while ignoring those
> multiple scatterings in this type of materials.
>
>
>

I'm not sure why those (or one of them?) is reporting "atoms too close
together".
You can control "how far out to go in R" with "RPATH" - is a value that is
smaller than the cluster size.
That is, you could use something like

RPATH 5.25

to consider paths with distance (half-path lengths) up to 5.25 Ang.

You can use NLEG to set the maximum number of legs in a
mulltiple-scattering path. That is,

NLEG 2

would mean "single scattering only", but you might want to actually use 3
or 4.  The default is 8 (in Feff8 that is, it is 7 with Feff6).

Cheers,

--Matt
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