[Pw_forum] About the flattening of phonon branches
Hello I mean, for example in the case of ALAs?(P. Giannozzi et al PRB 43, 7231 (1991)), the LO mode in the Gamma-X direction is very flat (mentioned by the authors, too). Is it related to the long interaction caused by the band structure (Sokel & Harrison PRL 36, 61)? Sorry about the affiliation Thank You R. Ebraahimi Graduate Student- Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100616/13b3c9bb/attachment.htm
[Pw_forum] About the flattening of phonon branches
Hello everyone I have a question, i wonder what is the physics behind the?flatterning?of the acoustic and optical phonon branches in some specific directions of the 1st Brillouin zone of some of the crystals?? Thanks for any comment -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100616/3b2d2eb3/attachment.htm
[Pw_forum] About the "pseudo-gen.txt" file
Hello Thanks a lot for your comments And specially to You Nicholas for providing the .pdf file. R. Ebraahimi -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100519/e8f38a41/attachment.htm
[Pw_forum] About the "pseudo-gen.txt" file
Hello everyone I found the file "pseudo-gen.tex" (in the atomic_doc folder of the code) very usefull, but i have problem with following it's strange notation (in the formula sections).?Is there any pdf format of this file? Could anyone refer me to an easy-to-read-version of it? Thank You? R. Ebraahimi Grad. Student- Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100519/5320fe44/attachment.htm
[Pw_forum] LO-TO splitting
Hello everyone i am trying to obtain the LO modes for an ionic crystal. All the irreducible reresentations at the Gamma point are 1-dimensional (A & B).?There are plenty of?infra-red active modes?(B_u), so when i use dynmat.x with a given direction, i have plenty of LO modes which should be assigned to the?TO's. I want to know that what should i do to assign the LO's to the TO's? Does the overlap matrix (with elements equal to the projection of the eigenvectors of LO's?on the?TO's) works? Thanx for any comment R. Ebraahimi Graduate Student Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100221/7e835eea/attachment.htm
[Pw_forum] LO-TO splitting
Hello everyone i have a question about the LO-TO splitting. Imagine an insulator or semiconducting bulk material that has no degenerate phonon mode at Gamma point (no "E" or "T" species after diagonalizing the Dynamical matrix). Should this bulk exhibit LO-TO splitting? Cause in this case, the # of the optical modes becomes more than 3N-3, right? Thank You in Advance R. Ebraahimi Graduate Student- Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100207/ff2c6e9a/attachment.htm
[Pw_forum] About Debye Temp.
Hi I am trying to investigate the Debye Temp. of two polymorphs of a non-metal case, by calculating the heat capacity,?c_v?(using the phonon DOS) at very low temperatures. But the polymorph with higher Bulk Modulus, gets the lower Debye Temp. I think, as the acoustic frequencies have more important role in both stiffness and "c_v in low temps", the higher the Bulk Modulus, may get the higher Debye temp. Am i right? Is there anything wrong in my calculation? Thanks for any comment R. Ebraahimi Grad. Student Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091028/9855250f/attachment.htm
[Pw_forum] gap in the phonon DOS
Hi Thanks for your reply What i meant to say was, does not the ionicity (Born charges and ..) of the crystal, which splits the TO-LO phonons, show itself as a gap in high-energy region of the phonon DOS? If not, what is the sign of this splitting?in the phonon dos diagram? Thanks again R. Ebraahimi Grad. Student- Tehran Uni. > Does the existence of a gap in the high-energy region of the phonon DOS > > means ionicity of the? crystal No, does not. It means just the mass difference, i.e. one of compound componenet is rather light, than other(s), as examlpe, NiAl, FeAl, FeH, PdH, etc. > (splitting of the TO and LO-like phonons)? This one is more relevant for the ionicity issue. This happens in polar semiconductors/insulatoras. Another excitnig example is gamma-boron phase where a cage of B-atoms (icosahedra, B12) is charged negatively, but dumbbell B-atoms B2 are charged positively giving rise for LO-TO splitting. > The higher the gap, means the more ionicity? The gap depends on both? the Born effective charge and static dielectric constant (see any textbook, or Rev.Mod.Phys. 73, 515, 2002, see page 527). So, the gap is the result of the competition of these parameters.? I suppose analyzing this relation for yourself will give you more insight.? Hope this helps. Bests, Eyvaz. --- Prof. Eyvaz Isaev, Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden Condensed Matter Theory Group, Uppsala University, Sweden Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com ? ? ? ___ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091025/3df80cac/attachment-0001.htm
[Pw_forum] gap in the phonon DOS
Hi I have a question. Does the existence of a gap in the high-energy region of the phonon DOS means ionicity of the crystal (splitting of the TO and LO-like phonons)? The higher the gap, means the more ionicity? Thank You for any reply Reza Ebraahimi- Graduate Student Tehran University? -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091024/26f9be6f/attachment.htm
[Pw_forum] About the input file for matdyn.x
Hi i have a question. imagine we have defined?a structure?by using?celldm(1)="a_0" and cell_parameters(1,1)="b",?so?the first bravais lattice vector's value?becomes "a_0*b". In the file matdyn.f90 is written "nq: q-points in 2pi/a units", is "a" in the mentioned description, the "a_0" or "a_0*b" ? Thank You Reza Ebraahimi Graduate Student- Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091011/4ec92fe0/attachment.htm
[Pw_forum] strange results in phonon calculation
Hi Trying to?run phonon calculation at Gamma point for my case, the code gives the following result for?some of the modes:? omega( 1) =*** [THz] =*** [cm-1] omega( 2) =*** [THz] =*** [cm-1] omega( 3) =*** [THz] =*** [cm-1] What does these mean? How should i fix this? Thanx Reza Ebraahimi - Graduate student Tehran University -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090407/a25aec0c/attachment.htm
[Pw_forum] ASR
Hi can anyone refer me to some literature about history of acoustic sum rules? i mean when was it proposed for the first time? and it's versions known here as "simple" and "crystal"? Thank You -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20081225/1cb85b39/attachment.htm
