*I am very sorry to re-send my email, but I really need to know the answer.*
Dear Siesta users, I am sorry, I have not got my answer reading the whole archive about this subject. Therefore, I hope you would kindly let me know the answer of the following question: We all know that for the crystals we have the following relation: *Cohesive Energy (CE) = (energy of free atom) - (energy of atom in a crystal).* I am working on GaN bulk and nanostructures. 1. Regarding the energy of the free atom, as I read the archive, it seems that we have to consider the ghost atoms surrounding the main atom to get the enrgy of the free atom?! or, it is enough to have the right basis of the atom and calculate its energy? 2. energy of atom in a crystal: when we calculate the enery of the bulk, then how do we have the energy of the atom in the structure? 3. I would be grateful if you let me know the additional terms I have to consider in order to calculate the cohesive energy of a slab too. Regards, Sarah
