Hi Fuxiang,

On Thu, Jun 23, 2016 at 11:38 AM, Fuxiang Zhang <zhangfx@umich.edu> wrote:

Hi, All,
I am new in using EXAFS techniques. Just wondering how to input atomic structure of NiFe solid solution to Artemis. It has a simple Ni-structure, but both Ni and Fe occupy the same site. If I use partial occupancy, Artemis program does not allow. Anyone can give me an ideal?

The concept of "partial occupancy" for a representation of a crystal does not really work for modeling EXAFS. Instead, to model EXAFS, you make a cluster of atoms, each of which has X, Y, Z positions and a fully determined atomic number -- an atom cannot be half Fe and half Ni.

You can start with a crystal structure of a full occupancy crystal and create a cluster of atoms from that, then EDIT this representation of that cluster (held in feff.inp) to build a cluster with some atoms moved, replaced by other species, etc. Editing feff.inp is sort of a common answer on this list, and I'm sure that an internet search will give you directions. You may even find

https://bruceravel.github.io/demeter/artug/extended/dopants.html

from the Artemis documentation helpful. ;).

Also the coordination number N cannot be refined in this simple system (12), is that right?

No, that is not right.

In fact I just want to get the N through the fitting of EXAFS because of the partial occupancy.

One can get partial coordination numbers from EXAFS analysis.

As Anatoly points out, distinguishing "Ni-Ni" from "Ni-Fe" or "Fe-Fe" will be extremely difficult.

Hope that helps,

--Matt