Dear IFEFFIT List, I learned that IFEEFIT can model a single absorber in two different environment. Could anyone direct me to similar studies that have been done or related tutorials? Below are some thoughts and questions: For example, there is 2 wt% A in both M1 and M2 structural sites in crystal X as dopant. I first create 2 FEFF models in Artemis, one has absorbing atom A only in M1 site and the other one has A only in M2 site. In the fitting process, is it correct that I choose paths from both FEFF models and using different Eo and So^2 for M1 and M2 sites? And to model the site occupancy of A in each site, I can create a fraction parameter "a" (which means there are a*2 wt% A in M1 site and (1-a)*2 wt% A in M2 site). Is it correct to apply this fraction parameter only to So^2 to model the site occupancy of A in M1 and M2 site? I am worried this approach will use too many variables. Any suggestions on the constraints/restraints that I can use? Finally, is there anything else that I missed which needs to be considered to do the modeling for this case of two different absorbing atom sites? Any suggestion will be greatly appreciated! Thank you all in advance! Best regards! Yun