Integrated absolute spin density

[Hui Li]

Dear CP2K users and developers:

I am using cp2k to calculate a O2 molecule absorbing on a gold
cluster. My system should have 3 unpaired electrons, and I give spin
multiplicity = 2. Because I use mixing and smear in SCF section, I
can't get the information of S**2 in my result.
And the information of spin in the output file is that:

  Integrated absolute spin density  :
2.7410711422
  WARNING: S**2 computation does not yet treat fractional occupied
orbitals

My question is that, what is Integrated absolute spin density? And how
to judge if there is any spin contamination in my calculation?

Thanks a lot!

Hui Li