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