Dear Pablo, I tried to play with your structure and I succeeded. First, run x supercell always one cell in x- y- and z- directions zero shift in all directions Enter your target lattice type: P (you must choose primitive lattice in order to break the symmetries you do not want there). Zero vacuum in all directions. Then cp TiO2-sup_super.struct TiO2-sup.struct Edit the TiO2-sup.struct file and find the two Cu atoms. Rewrite the space after first Cu to 1. Rewrite the space after second Cu to 2. Or do these two things comfortably using w2web. You must have them inequivalent. By the way, are you sure that the vacuum you have for your slab is sufficient? When I use slabs I try to have vacuum around 20 bohrs. Then run x sgroup By checking TiO2-sup.outputsgroup you see that sgroup has chosen monoclinic lattice but with all three angles equal to 90 degrees. (Space group 56 6 Pm) Then, I STRONGLY RECOMMEND TO ERASE ONE OF THE Cu ATOMS, probably the one at the position 0 0 0. It worked on my computer. HTH Tomas
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