Precision of Plane-Wave Pseudopotential Method¶
The user can enter the kinetic energy cutoff of the plane-waves used to represent the electronic wavefunctions.
Charge Density Cutoff¶
The user can also set the kinetic energy cutoff for the electronic charge density and potential.
Electronic Occupations and Smearing¶
An artificial thermal broadening of the Fermi surface of metallic materials is typically necessary in order to obtain smoother electron occupation distributions than the original step function, thus making the convergence of properties that need to be integrated across the Fermi surface more effective.
The different implementations of this "electron smearing" technique, as well as other methods for treating electronic occupancies which might be more suitable for semiconductors and insulators, are reviewed starting from page 175 of Ref.  linked in this page.
For a more in-depth explanation of the theory cited above, the reader is referred to the general review literature on the plane-wave pseudopotential formulation of Density Functional Theory listed in the corresponding references page.