and how many kpoints should we select for a 2x2x2 supercell having 52 atoms for phonopy calculations?
Maybe you can find your answer with Professor Mohammad Saeed Bahramy on his research gate page hope it's helpful.
Dear Saeed Ul Haq Khan
The best way to answer this question is performing several single point calculations using the unit cell with different K-points (e.g. 1-1-1, 3-3-3, 7-7-7, 11-11-11...) until you get convergence in the total energy, and always starting with just gamma point (to avoid very expensive calculations, maybe a few k-points is enough for your system!)
Probably if you are dealing with a metallic system you will need a higher number of kpoints than if you have an insulator.
Once you get the optimal value, if you have a 2x2x2 supercell, you can divide the number of kpoints by 2 (simple rule, if you double the size of the real space lattice, you need half of kpoints to describe reciprocal space!)
Hope it helps,
Fernando
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