Stefano de Gironcoli wrote: >Nicola Marzari wrote: > > >>6) this open up my favourite question - should B be spherical or >>cylindrical in DFT ? I.e. should we look like for occupation 1 0 0 >>for the 2p levels, or 1/3 1/3 1/3 ? >> >>7) Last, but important - even using Gamma sampling, PWSCF finds >>for your geometry 16 symmetry operations, and thus heavily >>symmetrizes the system. That means that in 6) even 1 0 0 would >>become spherical. I.e. the symmetrization has a similar effect >>to temperature, in creating a charge density that is more symmetrical >>/degenerate occupations than it could be. >> >>I would be *Very curious* to see what happens if you were to >>put the dimer in a very random position, so the code misses most >>of the symmetry operations, and also you specify no_sym, so no >>symmetrization is performed. >> nicola\ >> >> >> >> > I agree with Nicola that this is very relevant and that symmetrization > induces > a degeneracy that could not be there in the best "broken symmetry" > solution. > This one can be achieved by 1) occupations='from_input' 2) nosym=.true. > no smearing is required then. > I agree that symmetrization (due to the periodization) induces a degeneracy but the "real" system that I want to simulate (a dimer alone in space) has even more symmetries. In particular it has a rotational symmetry that will never be there in a periodic code!! life is hard:-) Anyway I will try to put the dimer in a random position to see what happens.
Systems with discrete levels are always a bit tricky and often present multiple solutions.. cyrille
