I want to understand, what is the intuition behind using the occupations='smearing' or 'tetrahedra' in Quantum ESPRESSO input file? I mean how we can interpret what is going to happen inside of crystal structure if I choose this option? How it will affect the band structure and how electrons are going to be filled in orbitals? I want to understand the connection between this input option and its effect on crystal structure.
Please, clarify my doubt.

  • $\begingroup$ I don't know much about quantum espresso, but is it a zero temperature method? $\endgroup$ Oct 7 '20 at 10:45
  • $\begingroup$ @taciteloquence, yes, it performs DFT calculations with plane-waves basis which is a theory for groud state properties of materials. $\endgroup$
    – UJM
    Oct 7 '20 at 18:00
  • $\begingroup$ Related physics.stackexchange.com/q/360037/262543 $\endgroup$
    – Thomas
    Oct 8 '20 at 4:39
  • $\begingroup$ @UjjawalM., in that case, I have no idea, haha $\endgroup$ Oct 8 '20 at 16:37

Smearing is a mathematical trick implemented in codes like quantum ESPRESSO so as to aid in convergence. It has no physical meaning. You could think of it as follows:

The orbitals are populated by electrons if the smearing is zero then the electrons are forced to acquired a set of finite energies without any tolerance factor to account for the error in the predicted energies. But with smearing turned on, you are essentially filling in fractions of an electron in some spread of energies within the vicinity of your original energy level. This helps in bringing in that error tolerence which is needed for convergence.

Hope this helps :)


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