CCL: Negative Ionization potential

 Sent to CCL by: "Morgan  Durand" []
 Dear All,
 I have to compute ionization potential for neutral or ionic forms via DFT. I
 benchmarked several functional and basis set based on litterature data (Fu &
 al., JACS 2005, 127, 7227-7234). Finally, I used TURBOMOLE associated with PBE0
 def2-TZVPPD for final energy calculation. Computed IP are very close to the
 litterature data (both experimental and calculated).
 Lately, I computed IP for almost 100 compounds. For some of them, DFT
 calculation leads to negative ionization potential.
 What does it means ? That something went wrong in my calculation ? Or that these
 compounds can't be ionized ? Anything else ?
 Thanks in advance,
 Best Regards,