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Dear everyone,

As said in the guide book ismear should be set to Zero for semiconductor or insulator system.But for metallic system it is better to be set as 1 or 2.Well,if I don't know whether a system is metallic or semiconductor,or some dopants may change metallic system to semiconductor,how should I set the value of Ismear at first.

Many thanks!

do a single electronic scf run without ionic relaxation (ISMEAR=-5) first and have a look at the electronic structure of that run.

when the system is so large
can we still use ISMEAR=-5?

you have to take enough k-points to cover the BZ with tetrahedra, than you can use ISMEAR=-5 of course.

For accurate bulk relaxation (for insulator and semiconductor), is it appropriate to use ISMEAR=-5 for relaxation in the first step if there are enough k points to cover the BZ with tetrahedra?

It says in the manual to use either 0 or 1.

relaxations with the tetrahedron (Bloechl) method should only be avoided if the system is metallic , or if the cell is so large that the number of k-points is not sufficiently high to construct the tetrahedra. So, if you have enough k-points, use ISMEAR=-5