Contribution of $\pi$-bonds to effective charges, cohesive energy, and force constants of graphene-like compounds

For 14 two-dimensional hexagonal compounds IV–IV and III–V, analytical expressions have been obtained using the Harrison bond-orbital method for the contribution from the $\pi$-interaction to the polarity of interatomic bonds, the effective atomic and transverse dynamical charges and their dependences on the deformation, as well as to the binding energy, the cohesive energy, and the central and non-central force constants.