  We investigate the chemical bonding characteristics of the transition metal
dichalcogenides based on their static and dynamical atomic charges within
Density Functional Theory. The dynamical charges of the trigonal transition
metal dichalcogenides are anomalously large, while in their hexagonal
counterparts, their sign is even counterintuitive i.e. the transition metal
takes the negative charge. This phenomenon cannot be understood simply in terms
of a change in the static atomic charge as it results from a local change of
polarization. We present our theoretical understanding of these phenomena based
on the perturbative response of the system to a static electric field and by
investigating the hybridization of the molecular orbitals near the Fermi level.
Furthermore, we establish a link between the sign of the Born effective charge
and the $\pi$-backbonding in organic chemistry and propose an experimental
procedure to verify the calculated sign of the dynamical charge in the
transition metal dichalcogenides.
