Hello Sarah, Never did that type of calculation, so please sages out there correct me if I'm wrong ...
Let say you want to calculate Fe, which is bcc. 1st, perform a calculation with the standard, cubic, two atoms unit cell. 2nd, perform the same calculation (keeping lattice parameter, basis, etc) but putting ghosts at the vertices, namely, keeping only the atom at the center. Finally, compare the two and you'l get the cohesive energy. Best, Roberto On Thu, 12 Feb 2009, Sarah Lebedev wrote:
*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
