Thanks Stefano and Nicola. Your anwsers are so professional and very helpful. As your comments, i guess Gamma point used in the large disordered materials and liquids can improve the calculational efficiency twice as fast. And for symmetric crystal, Baldereschi point works better. Am i right? And i did not find the Baldereschi point in PWscf, so it is not implemented here?
Thanks. In your mail: >From: Stefano de Gironcoli <degironc at sissa.it> >Reply-To: >To: Jiayu Dai <daijiayu at nudt.edu.cn>, PWSCF Forum <pw_forum at pwscf.org> >Subject: Re: [Pw_forum] Baldereschi and MP point. >Date:Wed, 17 Mar 2010 16:19:58 +0100 > >Dear Jiayu Dai > >the Baldereschi point and MP points are efficient choice because they >exploit the SYMMETRY properties of the system in order to sample the BZ >on a hopefully small set of points. >In liquid and disordered materials there is no symmetry and therefore >there is no symmetry-related k-point reduction and any regular grid of >points should be equally efficient. >On the other hand for large systems the BZ shrinks and the refolded >bands in the mini-BZ are almost flat which means that any single point >in the BZ should do the work. >In this situation Gamma is convenient because wfc (in absence of >spin-orbit) can be chosen as real in real space which implies that wfc >Fourier components of G and -G are related by complex conjugation and >you can use half the memory storage and cut by two the number of operations. > >best, > stefano > >Jiayu Dai wrote: >> Dear users, >> >> I have a question about the sample points in the Brillouin zone. We usaually use >> the MP point in our calculations, and it works well and fast in cubic >> crystal. >> However, for disordered materials or liquids, we usually use Gamma point >> only, >> such as point in CPMD. My question is how do we know the Gamma point is >> better >> than the Baldereschi mean value point, or on the contrary??Which one gives faster >> convergence? >> >> Thanks a lot. >> >> Jiayu >> >> >> >> >> ------------------------------ >> ------------------------------------------- >> Jiayu Dai >> Department of Physics >> National University of Defense Technology, >> Changsha, 410073, P R China >> ----------------------------------------- >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> > > > ------------------------------ ------------------------------------------- Jiayu Dai Department of Physics National University of Defense Technology, Changsha, 410073, P R China -----------------------------------------
