[Pw_forum] Cohesive Energy of N2 molecule

[Davide Ceresoli]

On 05/03/2011 05:54 PM, Izaak Williamson wrote:
> Dear all,
>
> I am trying to calculate the cohesive energy of the N2 molecule using the
> attached input file (relax.in <http://relax.in/>) and am getting a value of
> -16.57 eV. I use DFT with GGA and the pseudo-potential N.pbe-rrkjus.UPF. Other
> work [Fuchs et. al., Phys. Rev. B 65, (2002)245212] has performed similar
> calculations and obtained values ~10.5 eV. They even list an experimental value
> of 9.76 eV. Why is my value so much higher? Is there anything in my input file
> that could be giving inaccurate results? Is it my pseudo-potential that is
> causing this problem?
>
> Thanks for any help.
Dear Izaak,
     how much do you get for an isolated N atom, spin polarized, same
cell, same pseudo, same cutoffs?
In an old output file I've got: -39.7039435178 Ry for N2 at equilibrium
and -19.48996768 Ry for the N atom. Therefore: -0.724 Ry = -9.85 eV
(N.pbe-rrkjus.UPF)

Davide