Dear Users. I have a question, it is regarding lattice dynamics simulations using CASTEP ( M.S. 6.0). I want to run simulations on lattice dynamics on surfaces of different materials. I have been reading papers in literature in which they specify that in order to do this I need several layers and slabs. Due to computational power, I am limited in this and I feel I cannot use more than 4-6 layers, is it possible to obtain dispersion curves and phonon DOS on such a thin surface ? I followed the tutorial on CASTEP but when I am try to analyze the results the files are not available. I read a forum in which they said this type of simulations can only be performed on an unit cell ( due to  ymmetry). However, I have read several papers in which they specifically mention the surface phonons, dispersion curves and vibrational analysis. How can I perform this type of simulation using CASTEP or DMOL3. My system is LiAlH4 [001] facet ( complex metal hydride).

Thank you very much for your kind help,

Fernando Soto