K-point grid and gaussian smearing

For each crystal you will need to specify what k-point grid you want to use to sample the Brillouin zone.

Example:

k_grid  4 4 4
k_grid_shift 0.5 0.5 0.5

This specifies a Monkhorst-Pack grid of 4x4x4 points shifted off by in reciprocal lattice vector units. This example is probably sufficient for most semiconductors with a smallish unit cell. If you have a large unit cell, you need fewer k-points, and if you have a metal, you will need a lot more.

If you are calculating a metal, you should use gaussian smearing. This smears out the fermi level, so that more of your k-points will be effectively on the fermi surface. The gaussian_smearing is specified in eV. If you are calculating an insulator, you should set gaussian_smearing to be some small value.

Example:

gaussian_smearing 0.05