k-points convergence

How can I know the number of k-points that I should use for my system?

As a rule of thumb for choosing the initial k-point sampling one should consider the product between the number of k-points in a given direction (ki) and the length in Angstrom if the basis vector in that direction (ai) and take this product as Lithe initial number of k-points:

  • kiai ~ 30 Å, for d band metals
  • kiai ~ 25 Å, for simple metals
  • kiai ~ 20 Å, for semiconductor
  • kiai ~ 15 Å, for insulator

Remember that the convergence of this parameter should be checked.

You may find here a helpful SIESTA tutorial about converging the simulations, check point 1 (Convergence of electronic and structural properties of a metal with respect to the k-point sampling: bulk Al) and point 2 (Convergence of energetic and structural properties of an insulator with respect to the k-point sampling: bulk BaTiO3).