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Hi everyone,

I want to run optimization and frequency calculations for semiconductors. I need your suggestions for setting the ISMEAR tag. Now, I have two choices. (1) using ISMEAR=-5 for every calculations. (1) using ISMEAR=0 for optimization and frequency calculations and using ISMEAR=-5 for energy calculation. Can anyone compare the computational accuracy and efficiency between these two methods for me? Thanks!

Hi,
If your system is a semiconductor you should use ISMEAR=-5 because the forces are always correct, since partial occupancies do not vary. In that way, the total energy and DOS calculations are very accurate.
However, if you have a very large system, you can't use 4 k-points (needed for tetrahedron method, ISMEAR=-5) and you should use ISMEAR=0.