[Ifeffit] How to generate the input information for Atom

Hi, Bruce, I am working on an experiment of arsenic adsorption on pyrite particles. I have the data of mu(E)~E. I use Anthena to do the Fourier transform. Now I want to know the cordination information of arsenic atom. How can I get the input file for Atom if I want to do the fitting job by using Iffefit package? Thanks!