Thank you so much dear Lorenzo... On Tue, Oct 27, 2009 at 9:32 PM, Lorenzo Paulatto <paulatto at sissa.it> wrote:
> In data 27 ottobre 2009 alle ore 15:00:25, mohnish pandey > <mohnish.iitk at gmail.com> ha scritto: > > I can fix this problem by preserving the symmetry and > > getting eqb. lattice constan.? > > Dear Mohnish, > the code actually do preserve the symmetry, it is enforced actively when > computing the forces and cannot be broken during the relax procedure. > What's happening is that the system has a lower symmetry than you think > since the very beginning. > > There are two possible reasons: > 1. you have not specified the initial atomic positions with sufficient > precision, the code consider an atom to be in a high symmetry position if > it is less than 1.d-6 away from it (I think in units of alat=celldm(0), > but I would have to check) > 2. the symmetry of your system has a free parameter you where not aware > of, e.g. in a Wurzite structure the distance between alternate planes can > change in a specific way without breaking symmetry. > > These two problems have two corresponding solutions: > 1. specify more digits, or (with QE 4.1 and next) specify the position as > a fraction, e.g. > Ga 1/3 2/3 0 > note that xcrysden cannot yet interpret an input file written like this > and it is still a bit experimental > 2. lock the atoms in position, you can do that adding three zeroes after > the atom's coordinate in the input, e.g.: > Ga 0.3333333 0.6666667 0.000000 0 0 0 > have a look at the manual (Doc/INPUT_PW.txt) for details on details on > this notation > > best regards > > > > -- > Lorenzo Paulatto > SISSA & DEMOCRITOS (Trieste) > phone: +39 040 3787 511 > skype: paulatz > www: http://people.sissa.it/~paulatto/<http://people.sissa.it/%7Epaulatto/> > > *** save italian brains *** > http://saveitalianbrains.wordpress.com/ > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Mohnish Pandey Y6262,4th Year Undergraduate, Department of Chemical Engineering, IIT KANPUR -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091027/6ecf85bf/attachment.htm