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
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