Dear SIESTA Users,
I think that the "inability" of SIESTA to correctly describe LO phonons in polar materials such as AlN at the limit q tend to 0 is porbably due to the fact that this code uses atom-centred basis sets which fail to describe the long wavelengths near gamma well far from the the atomic centers. Karim this might be useful : http://chianti.geol.ucl.ac.uk/~dario/tutorial_phonons.tar.gz On Fri, Apr 15, 2011 at 12:48 PM, karim rezouali <rezoual...@yahoo.fr> wrote: Dear all, I am currently working on the phonons in the whole Brillouin -zone of bulk wurtzite AlN (VIBRA- supercell of 500 atoms) and I encounter a serious problem with LO phonons in the limit of gamma. I calculated the Born charges and the dielectric tensor (LO-TO spleeting) and the results (attached file: dipersion along gamma point- A point) do not agree with calculations reported in the litterature using other softwares (linear response method). I increased the size of the supercell (700 atoms) but no change in the shape of the LO branch was observed. Is the problem intrinsic to SIESTA because no works are available (to my knowledge) on the whole-Brillouin zone optical phonons using this code in the literature?!. Thanks in advance, Karim -- Mehmet Topsakal (Ph.D. Student) UNAM-Institute of Materials Science and Nanotechnology. Bilkent University. 06800 Bilkent, Ankara/Turkey Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365 http://www.researcherid.com/rid/A-5015-2010
