  A recent experimental study showed that, distorting a CoPc molecule adsorbed
on a Au(111) surface, a Kondo effect is induced with a temperature higher than
200 K. We examine a model in which an atom with strong Coulomb repulsion (Co)
is surrounded by four atoms on a square (molecule lobes), and two atoms above
and below it representing the apex of the STM tip and an atom on the gold
surface (all with a single, half-filled, atomic orbital). The Hamiltonian is
solved exactly for the isolated cluster, and, after connecting the leads (STM
tip and gold), the conductance is calculated by standard techniques. Quantum
interference prevents the existence of the Kondo effect when the orbitals on
the square do not interact (undistorted molecule); the Kondo resonance shows up
after switching on that interaction. The weight of the Kondo resonance is
controlled by the interplay of couplings to the STM tip and the gold surface,
and between the molecule lobes.
