  In our previous paper [J. Chem.Phys. {\bf 137}, 22A544 (2012)] we argued that
the Born-Oppenheimer approximation could not be based on an exact
transformation of the molecular Schr\"{o}dinger equation. In this Comment we
suggest that the fundamental reason for the approximate nature of the
Born-Oppenheimer model is the lack of a complete set of functions for the
electronic space, and the need to describe the continuous spectrum using
spectral projection.
