Spontaneous symmetry breaking by double lithium adsorption in polyacenes

We show that adsorption of one lithium atom to a polyacenes, i.e. chains of linearly fused benzene rings, will cause this chain to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite of the fact, that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.