work function and Fermi level

[dong0216]

Dear ATK staff and users:
      I have a question about work function,Fermi level and vacuum level. I have calculated the Fermi level and  work function of metel. However, i found that the  value of Fermi level  was different from work function, so i want to know that how are vacuum levels defined. Are the vacuum levels different in different systems?
     Looking forward to your reply. Thanks.

[Petr Khomyakov]

Please take a look at this tutorial https://docs.quantumatk.com/tutorials/work_function_ag_100/work_function_ag_100.html.

[dong0216]

           Thank you for your reply. I have other questions. First, i want to know that if i  use th same parameter setting, what is the relationship between the work function and the Fermi level. Second, i want to know that  the the work function is the bulk of metal or metal surface.
           Look forward to your reply. Thanks.

[Petr Khomyakov]

Work function is a property of metal surface, not bulk material, which is infinite by definition, i.e., has no vacuum region. It means that there is no relation between the Fermi energy of bulk material and work function of a particular surface. For a surface, the Fermi level can be defined with respect to the vacuum level. In this case, the absolute value of the Fermi energy is work function of that particular surface.

The actual problem is that there exists no absolute reference zero energy. That is why comparing absolute energies obtained in two separate calculations, e.g., for bulk and surface systems, makes little sense.