.. Artemis document is copyright 2016 Bruce Ravel and released under The Creative Commons Attribution-ShareAlike License http://creativecommons.org/licenses/by-sa/3.0/ The Path-like tab ================= One of the powerful features in :demeter:`artemis` is the ability to define :quoted:`path-like` objects. A path-like object is one which can be treated like a normal path from :demeter:`feff`. It can be used in a fit and it can be plotted. It is not, however, the result of a normal :demeter:`feff` calculation. Instead, :demeter:`feff` has been run in some special way to generate a theoretical |chi| (k) spectrum for something different from all the items listed on the Paths tab. :demeter:`artemis` defines a number of kinds of path-like objects. Controls for generating these things are divided into different pages accessible by the menu at the top of the Path-like tab. The first item in that menu is for defining :guilabel:`SSPaths`. .. _fig-feffpathlike: .. figure:: ../../_images/feff-pathlike.png :target: ../_images/feff-pathlike.png :align: center The Pathlike tab. Single Scattering Paths ----------------------- The concept of a :quoted:`Single Scattering Path` (or :quoted:`SSPath`) is that it uses the potentials from a :demeter:`feff` calculation to compute the single scattering contribution from an atom that exists in that :demeter:`feff` calculation but at a distance not represented in the list of cartesian coordinates. .. _fig-feffplotss: .. figure:: ../../_images/feff-plotss.png :target: ../_images/feff-plotss.png :align: center Plot of a path-like object. In the example shown, a :demeter:`feff` calculation has been run on LaCoO\ :sub:`3`, a trigonal perovskite-like material with 6 oxygen scatterers at 1.93 |AA|, 8 La scatterers at 3.28 |AA| or 3.34 |AA|, and 6 Co scatterers at 3.83 |AA|. Suppose we had some reason to wonder what a Co scatterer at a distance of 3 |AA| would look like in a fit. (For example, we might suspect that some phase segregation happened during synthesis, resulting in some CoO.) In that case, the distance on the :guilabel:`SSPath` page would be set to 3.0 |AA| and the Co scatterer would be selected from the group of radio buttons. This group of radio buttons corresponds to the list of unique potentials in the input data for :demeter:`feff`. The method for associating this :guilabel:`SSPath` with data will be explained in the `next chapter <../path/index.html>`__. For now, we simply look at :numref:`Fig. %s ` to compare the normal Co scatterer at 3.83 |AA| (blue) with the SSPath computed at 3 |AA| (red). Use of :guilabel:`SSPath` for modeling scatterers at such a long distance is much superior to using a `quick first shell theory <../path/pathlike.html>`__. The advantage of this approach is that it uses well constructed scattering potentials |nd| i.e. potentials from a real structure |nd| to make the special path. Using the quick first shell technique on a path this long results in poorly constructed potentials. This is explained in detail in `the extended discussions chapter <../extended/qfs.html>`__. The SSPath is discussed in .. bibliography:: ../artemis.bib :filter: title % "Muffin" :list: bullet FSPaths ------- Model the effect of variable forward scattering angle in nearly collinear multiple scattering paths. .. todo:: FSPaths have not yet been implemented. Histogram paths --------------- .. todo:: Document the histogram system.