  The coupling of a molecule and a cavity induces non-adiabaticity in the
molecule which makes the description of its dynamics complicated. For
polyatomic molecules, reduced-dimensional models and the use of the
Born-Oppenheimer approximation (BOA) may remedy the situation. It is
demonstrated that contrary to expectation, BOA may even fail in a
one-dimensional model and generally expected to fail in two- or
more-dimensional models due to the appearance of conical intersections induced
by the cavity.
