Hello, In EXAFS data modeling carried out by fitting excercise, we develop mathematical expressions for different path parametrs as functions of a smaller set of fitting parameters that can be adjusted to achieve to best fit to the data. I am carrying out EXAFS analysis of Eu(III) sorbed on different environmentally relevent mineral oxides. In conection of this i also analysed some reference standard compounds. In developing expression for different path parameters, though i developed the expressions using my own understanding and taking help from one of Shelly's tutorial regarding SnO2 case, i am not confident. Basically SS2, and deltaE expressions puzzle me. Could someone help me in understanding basic approach in developing their expressions(for reference Eu2O3 structure could be taken). Regards, Sumit