Dear Prof. Postnikov, Thank you for your suggestion and the excellent lecture is what I need now, thank you very much!
Best regards, On Mon, Jul 26, 2010 at 3:35 PM, <[email protected]> wrote: > > > > >>it is normal that as you increase your system to include many > >> >equivalent (or almost) atoms > > > > I do not understand why many equivalent atoms will affect the > convergence. > > Hi, > > I explained it already: > >> because of electrons flopping between nearly degenerate states. > In other words, the states just under the Fermi energy can be > occupied in different way, and the electrons are just shifted around, > without reaching the convergence. > > >>To get an idea, look at the results (Mulliken charges; DOS) > >> >underway, after some number of iterations. > > > > Could you give me some ditails about checking the results of Mulliken > > charges or DOS after some number of iterations? > > You print out Mulliken charges, there is a switch for it. > You look at them and think whether they are as you expect > (i.e., the atoms which ought to be magnetic are magnetic, > and in a right way). > Check if you find anything useful in the following lecture: > http://www.home.uni-osnabrueck.de/apostnik/Lectures/APostnikov-Magnets.pdf > > > Usually, I just check the following information of the scf. > > >--------------------------------------------------------------------------- > > siesta: iscf Eharris(eV) E_KS(eV) FreeEng(eV) dDmax Ef_up > > Ef_dn(eV) > > ...... > > siesta: 799 -32180.0924 -32180.0919 -32180.0919 0.0011 -3.0670 > > -3.0670 > > siesta: 800 -32180.0924 -32180.0919 -32180.0919 0.0011 -3.0670 > > -3.0670 > ... > > siesta: 826 -32180.0929 -32180.0925 -32180.0925 0.0010 -3.0669 > > -3.0669 > > siesta: 827 -32180.0931 -32180.0927 -32180.0927 0.0010 -3.0668 > > -3.0668 > > ...... > > This is good but does not tell you anything but that your calculation > is not quite converged. > In fact it doesn't look like a divergence, and the Fermi level(s) are > not a priori unreasonable. So, before doing anything else, try > to make sense out of your calculation (position of bands, magnetic > moments, etc.) > > > ---------------------------------------------------------------------------- > > > > I'd like to increase the DM.MixingWeight to 0.3 to accelerate the > > calculation. Is it correct? > > If it smoothly converges to a right solution, that's fine. > But I'd rather suggest, with system as large as yours, to be > more prudent. 0.3 is a huge mixing weight. > > > Since you said I need a small mixing > > parameter, > > how to understand the mixing parameter? I read some notes about > > DM.MxingWeight, but there is still something puzzled me. > > > > alpha has to be small (0.1-0.3) for insulator and semiconductors, > > tipically much smaller for metals. > > Yes; what is the problem? In metals you need a good sampling of states > near the Fermi level; imagine you have a narrow band which shifts > across the E_f; then you'd like to damp the resulting fluctuations. > In semiconductors the situation is (usually) less critical because > bands are either occupied or empty. > > > BTW, whether my setting of the antiferromagnetism is correct. > > I don't know the structure, sorry. Apart from this - yes; > some Fe atoms marked "+" and others "-", as it should be. > > Best regards > > Andrei Postnikov > > -- Bin Shao College of Information Technical Science, Nankai University 94 Weijin Rd. Nankai Dist. Tianjin 300071, China Email: [email protected]
