For some time I'm using FEFF8.4 for calculations of absorption-XANES and DOS in some superconducting materials for which it has been successful, now I have the need to include in the'' input "of some impurity atoms in interstitial positions by Example: *A* *1.16* *B* where *A* and *B* are two different species of atoms, I made several attempts in trying to implement this using ATOMS3.0 on the web: http://millenia.cars.aps.anl.gov/cgi-bin/atoms/atoms.cgi but I have not had consistent results, in ATOMS3.0 manual explains that the program has been designed for this, but suggests that it may be possible. I appeal to you to see if I can help solve this problem. Thanks for your attention. Diego Fernando Mulato Gómez. Estudiante de doctorado en Física Teórica, CINVESTAV, Unidad Mérida, México.