Dear Sandeep, sure it can, if you take all the periodic replica of any atom into account (as one should).
SB On Jun 30, 2011, at 7:28 PM, Sandeep Kumar wrote: > Dear PWSCF users, > I have carried out linear response phonon calculations for Al over a 4 * 4 * > 4 grid of q-points. This corresponds to a calculation in a supercell > comprised of 4 * 4* 4 unit cells (primitive). > We recall that the lattice vectors in fractional coordinate system of a fcc > primitive cell are- > a=(0.5, 0.5, 0.0) > b=(0.0, 0.5, 0.5) > c=(0.5, 0.0, 0.5) > >> From the force-constant file (Al44.fc) I obtained the force constant matrix >> Phi(i1,i2, na, nb) for pairs of atoms in the super-cell with the relative >> positions given by > R = (i-1)*a + (j-1)*b +(k-1)*c > where i j and k are read from Al444.fc file. > However, such a supercell does not include the pair of atoms located along > the cube axis direction i.e R = (a,0,0) or (0,a,0) or (0,0,a), and hence the > calculation CAN NOT give us the force-constant matrices along those pair of > atoms. > How do we obtain the force-constant matrices for pair of atoms located along > the cube axes direction. > I will be VERY VERY GRATEFUL to any help in this regard. > > Sandeep K. Lahiri > Department of Mechanical Engineering > Massachusetts Institute of Technology > Cambridge, MA > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110701/52fb8640/attachment.htm
