  Despite the great success of density functional theory in describing
materials, there are still a few examples where current exchange-correlation
functionals fail. We add another example to this list that drives further
development of functionals. We show that the interaction of O$_2$ with Ag(110)
cannot be properly described by some of the most popular GGA, meta GGA, and
hybrid functionals. We identify problems and provide clues for a functional
that should be able to describe this and similar systems properly.
