Dear friends, just a small update for the potential scanning stuff: It works fine for one shell. Really straightforward thanks to the ifeffit() calls. Some corrections and I can provide you the program ;) But there is one little thing I am thinking about, which is fairly general, I think: If I just have one shell, everything is fine. The program iterates through all possible variable combinations. But... if I have two shells I just manage to let him vary the shells independently. I know there must be a way to tell the algorithm that if there are 2 shells it needs to vary each of the eight parameters against each other and not two times the four from each shell. I know there are some good PERL hackers around. So do you have an idea how to do this? Recursion shurely helps - I experimented a lot with it but it still does not do what I need it to do. Just for your convenience: I stored the parameters in an array of hashes, so that I can have something like $shell[0]{E0} = $something $shell[0]{dr} = $somethingelse... So the loop for one shell is just looping through the hashkeys of element 0 of this array... Thanks for your suggestions. Cheers, Norbert -- Dr. rer. nat. Norbert Weiher (norbertweiher@yahoo.de) Laboratory for Technical Chemistry - ETH Hönggerberg HCI E 117 - 8093 Zürich - Phone: +41 1 63 3 48 32