I wants to optimize MoS2 nanotubes, I am using ISIF =2 and changing POSCAR using Selective dynamic option ie (0.25 035 078 F F T). I am not relaxing the ions in x and y direction.Is it correct assumption in case of nanotube? .Please provide some reference .I have try both options using selective dynamic option and without this there is only change in Total energy, the energy of the the tube without selective dynamics is more then of selective dynamic option. You are requested to please suggest correct way with reference.