Hi Renske, I am not sure whether I fully understand your question but here is my *two-cent-explanation*: FEFF's first step is to calculate the potentials - since it is a real space code based on the muffin-tin approximation the surrounding of an atom determines the actual scattering potential (even if you are not doing a self-consistent calculation). Since the potentials in turn determine the backscattering amplitudes and phase shifts, placing an additional atom randomly in a structure is certainly not a good idea. A possible work-around may be to find a *similar* (but known) structure with oxygen ligands and combine these two calculations in artemis (for multiple scattering however the geometry can matter a lot). If your solvent contains oxygen already you may (at least as a first approximation and for single scattering) just duplicate that path in artemis. Regards Jakob ___________________________________________________ Jakob Frommer Soil Chemistry Group Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich Universitätstrasse 16, CHN F19 CH - 8092 Zürich Tel: +41 44 632 87 58 Fax: +41 44 633 11 18 web: http://www.ibp.ethz.ch/research/soilchemistry