First principles study of polyatomic clusters of AlN, GaN, and InN.: 2.: Chemical bonding

In this paper we study the chemical bonding of the small (monomer, triatomic, and dimer) neutral clusters of AlN, GaN, and InN presented earlier in paper I. It includes the analysis of the topology of the electron density and its Laplacian, together with relevant atomic properties, in light of the theory of atoms in molecules. The most prominent feature of the bonding here, the existence of strong N-N bonds, is seen to diminish with an increase in the number of metal atoms and the degree of ionicity. The Al-N bond shows a large transfer of charge, but also a significant deformation of the Al electron shells, so it can be understood as a highly polar shared interaction. On the other hand, Ga-N and In-N bonds are nonshared interactions, with smaller charge transfers and polarizations. In all cases, the existence of a N-N bond weakens the metal-nitrogen bond. The bonding picture that emerges depends only on the reliability of the electron densities, and it is consistent with the conclusions of,our previous work in paper 1.