[Wien] PLEASE HELP-Simulation of muliple element ELNES of binary composition materials

[a s]

Hello Folks

I am running Wien2K_03 on a Pentium 4 2GHz machine with a Red hat Linux 7.3 
operating system.

The purpose of my calculations is to simulate the carbon k-edge and nitrogen 
k-edge ELNES of graphite with a low concentration of individual C atoms 
substitutionally replaced by N atoms.

In order to do this simulation, I have constructed a supercell consisting of 
8 atoms, with one C atom replaced with a N atom.  The entire calculation 
runs perfectly from start to finish, providing a graphite-like carbon ELNES, 
as expected.

However, when I try to produce the associated nitrogen ELNES, I run into 
difficulties.  I try to produce the associated nitrogen ELNES by following 
exactly the same procedure as for simulating the carbon ELNES, apart from 
modifying the ‘E-loss of 1st edge” parameter to 400 eV in the step ‘Edit 
input-file for ELNES’.  I then obtain exactly the same nitrogen ELNES as the 
carbon ELNES!

I note from the Jan 2005 archive, that in a posting by Shu Miao (“EELS of L3 
Ti edge”) that he was advised, “You should never have more than one 
excitation in your cell. The inelastic cross section for core loss is really 
very small, and not that many excitations occur.  Additionally, the small 
spatial extent of the core orbital 'localizes' the event, and there is no 
need to consider several simultaneous core loss excitations.

If your two oxygen positions were inequivalent, they would have different 
initial/final states and therefore a different spectrum.  So you would have 
to do two separate calculations (one for each inequivalent oxygen), and then 
sum the spectra to get the 'total spectrum' of your material.  (That is not 
the same as exciting both atoms in one single calculation!)”

Does this mean if I wish to simulate BOTH the carbon AND nitrogen ELNES of 
graphite with a low concentration of individual C atoms substitutionally 
replaced by N atoms, that I have to do two separate calculations?

Any advice gratefully appreciated.

Kindest Regards

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