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Using this input
Cu FCC vc-relax method error to calculate Ebulk, I'm trying to calculate the cohesive energy of solid Cu (Ecoh = Eatom − Ebulk). For the Eatom I'm using a similar input but with '

     calculation = "scf", 

      ibrav = 1, 
       
      celldm(1) = 30.0,

      K_POINTS (automatic)
       1 1 1 0 0 0

I'm getting Eatom=-212.83147680 Ry and Ebulk = -213.09295997 Ry. Which will give an Ecoh far from the 3.49 eV (the literature value http://www.knowledgedoor.com/2/elements_handbook/cohesive_energy.html).

Could this be related to the pseudo I'm using (Cu.pbe-dn-kjpaw_psl.1.0.0.UPF)? Or do I need to modify my input files?

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1 Ry is roughly 13.6 eV, so actually you aren't that far off in that calculation. You find a difference of roughly 0.26 Ry, which multiplied by 13.6 will give you 3.54 eV. This is a pretty good match considering although you may get different numbers with different psuedopotentials.

I will say though, your input file for both calculations differs by more than it should. You will need to make sure everything you apply to the bulk, is applied to the gas phase atom, except for some things such as the cell relaxation and the kpts should be (1, 1, 1). You should make sure that energy cutoffs, functional, etc match exactly or your calculations are not comparable.

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