This tutorial explains how to perform the convergence study with respect to the number of k-points and smearing width, and how to analyze the electronic structure, i.e., band structure and density of states.
Metallic systems have the Fermi surface, and to handle it, STATE uses the smearing technique with various smearing functions and the tetrahedron method. Furthermore, the number of k-points to sample the Brillouin zone can be critical for the accurate calculation of the metallic systems.
Here we present the convergence of the total energy with respect to the number of k-points with the Methefeesel-Paxton smearing (default) and tetrahedron methods. Use negative WIDTH (e.g. -0.02) to activate the Methefessel-Paxton smearing (with positive value, a parabolic function is used to treat the Fermi level and the entropic term is not taken into account).
Total (free) energy of the metallic system is sensitive to the smearing width, in particular, with the Gaussian and Fermi-Dirac function. Here we demonstrate the smearing width dependence of the total energy, following the seminal work by de Gironcoli [Phys. Rev. B51, 6773(R) (1995)].