First of all thank you very much for the suggestions, now I can reach convegence quite easily. The results should be correct: I have compared them with other calculations and for example the, charged, relaxed configurations are the same as those obtained with other meathods that I know are right. But I am still puzzled by the electronic structure: In Si5H12 with no extra charge the homo is the 16th level and I expect that if I add an electron the homo will be the 17th energy level and that it will be half filled. Neverthelss the Fermi level I obtain is still in between the 16th and 17th energy level so the homo is still the level 16! What makes me think that the result is anyway correct is that the Fermi energy is very near to the level 17 (but below it) so since I am adding some smearing (300K of electronic temperature), maybe the 17th energy level is actually occupied. Is my reasoning sound, or the Fermi energy should be abouve the 17th energy level? May I ask a brief explanation on how the Fermi energy is calculated and how the extra charge is added (and remooved)? Thanks again for past and eventual future help,
Luigi. 2013/6/3 <[email protected]> > Dear Luigi, > > Si5H12 has an even number of electrons, therefore > when adding or removing one, in principle, you ought to use > spin polarized = true. > (This will become less and less crucial as you increase > the system so it becomes more "solid-like" and/or metallic. > But at the beginning this extra electron is likely to be > carried by a isolated level in the gap, I guess). > A bad convergence is probably due to swapping between > competing states, where this extra electron is differently > allocated in space. This might be a manifestation of > a genuine physical problem in a sense that, > given the symmetry of your system, the level in question > may want to be degenerate (jus a guess...) whereas you > populate it with a single electron. If this is indeed the case, > a small distortion may help to fix the issue... However > "in real world" you'd need to allow spin-orbit interaction > to get it right. > > By setting spin polarization off you cheat the system and tell it > to search only among doubly degenerate states. The result may > converge better, but place the energy level at a wrong place. > It could be useful to have a look at where the levels are > (where your extra charge is sitting) and try to make sense > out of it. > > If not caring about all above, but just technically > aiming at convergence, I'd suggest you to > i) reduce the mixing factor considerably, > ii) first set ElectronicTemperature higher (say to 600 K) > to facilitate convergence, and then gradually decrease it. > > Moreover the MeshCutoff of 150 Ry might be not high enough > to get a good physical result, and might also affect the convergence. > > Good luck > > Andrei Postnikov > > > > Hello everybody, > > I am trying to perform a calculation of a charged system composed of a > > molecule of Si5H12 > > with an extra electron (and in the future also one less electron) so I > > set: > > > > NetCharge -1.00 > > SpinPolarized .true. > > FixSpin .true. > > TotalSpin 1.0 > > > > But the calculation even for this small system does not converge. > > If I put SpinPolarization .false. the calculation converges rapidly but I > > am not sure that it's correct. > > recently I added also: > > > > SimulateDoping .true. > > > > It helps only slightly but convergence is still far from beying achieved. > > These are the other parameters of my input file: > > ---------------------------------------------------------------------- > > SystemName SiH > > SystemLabel SiH > > #(1) SPECIES AND ATOMS > > NumberOfAtoms 17 > > NumberOfSpecies 2 > > %block ChemicalSpeciesLabel > > 1 14 Si # Species index, atomic number, species label > > 2 1 H # Species index, atomic number, species label > > %endblock ChemicalSpeciesLabel > > #(2) FUNCTIONAL > > xc.functional GGA > > xc.authors PBE > > SpinPolarized .true. > > FixSpin .true. > > TotalSpin 1.0 > > MeshCutoff 150 Ry > > NetCharge -1.00 > > SimulateDoping .true. > > #(3) BASIS > > PAO.SplitTailNorm .true. > > #(4) SCF OPTIONS > > MaxSCFIterations 4000 > > DM.MixingWeight 0.01 > > DM.Tolerance 1.d-4 > > DM.NumberPulay 3 > > SolutionMethod Diagon > > ElectronicTemperature 300 K > > #(5) MD OPTIONS > > MD.TypeOfRun CG > > MD.NumCGsteps 1000 > > #(6) OUTPUT OPTIONS > > #(7) CRYSTAL STRUCTURE > > LatticeConstant 30.0 Ang > > %block LatticeVectors > > 1.000 0.000 0.000 > > 0.000 1.000 0.000 > > 0.000 0.000 1.000 > > %endblock LatticeVectors > > #(8) ATOMIC COORDINATES > > AtomicCoordinatesFormat NotScaledCartesianAng > > AtomicCoordinatesAndAtomicSpecies < Si-H.siesta > > ---------------------------------------------------------------------- > > > > I hope someone has a hint. > > Thanck you very much in advance. > > > > L. > > > >
