Role of ISMEAR in insulator-conductor transition

小喽喽问

am working now with a transition metal oxides. When I change some oxygens and put nitrogen in its place, the electronic structure change from insulator to conductor. For total energy insulator’s bulk calculations I have used ISMEAR=-5 (tetrahedron method with Blöchl corrections), but when the solid become conductor I must use ISMEAR=1 or 2.

My question is: Do I must compare the energies got with diferent ISMEAR keeping the same all others parameters?

Other question related: Do I must get the DOS and total energy for a optimized conductor structure whih ISMEAR=-5 or with ISMEAR=1 or 2?

Other question related: I get occupancies of some states larger than 2 with ISMEAR>0 for conductors too. Then, What are exactly the problems derivated from to use ISMEAR > or = 0 for insulators and semiconductors?

Thak you so much

大牛答：

for very accurate DOS and total energy calculations ISMEAR=-5
always should be used.
if the electronic structure changes from metallic to insulating upon
substitution of certain atoms, please do the following
1)
– for the GEOMERTY relaxations of the METALLIC system, use
the Methfessel-Paxton method (ISMEAR =1 or 2)
– (for the insulating phase, ISMEAR=-5 can be used for the geometry optimisation)

2. if the structures are fully relaxed, do one final (electronic scf) step with ISMEAR=-5 for the metallic phase as well, without any further change in the geometry.

3. the DOS should be obtained with Bloechl’s method for both systems