ali kazempour wrote: > > Hi > I want to get binding energy of O2 mulecule .For this I need the > correct value for isolated atom energy. But when I change(reduce) the > smearing ,the value of energy increase. So I DONT know which smearing > should I use? the larger or the smaller? > thanks
Smearing is used primarily to smooth the fermi discontinuity in metals, allowing to use coarser meshes of k-points. From this point of view, for an atom you'll have gamma sampling and no k-points issues. A secondary effect of smearing is that it helps reach selfconsistency - especially in atoms or molecules where the HOMO and LUMO are close and could swap order during selfconsistency. What you want is to use a smearing that is quite a bit smaller than the converged HOMO-LUMO gap - when that happens, the HOMO is full, the LUMO is empty, and the energy E or the free energy E-TS do not change as you vary the fictitious smearing temperature T. If you have trouble reaching self-consistency in this case, use a larger smearing, and then restart from your converged results with the smaller one. nicola -- --------------------------------------------------------------------- Prof Nicola Marzari Department of Materials Science and Engineering 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
