The empirical nearest-neighbor tight binding theory and the Harrison bond-orbital model are exploited to investigate the variation in effective band gap, electron effective masses and dielectric constants induced by non-stoichiometry. A model is proposed to describe absorption edges in heavily-doped InN using the Efros-Shklovslii approach for compensated semiconductors and taking into account the non-parabolicity of the InN band structure. Reasonable agreement with experimental trends has been demonstrated.