Theoretical investigation on the electronic and geometric structure of GaN2+ and GaN4+

The electronic and geometric structures of gallium dinitride cation, GaN2+ and gallium tetranitride cation, GaN4+ were systematically studied by employing density functional theory (DFT-B3LYP) and perturbation theory (MP2, MP4) in conjunction with large basis sets, (aug-)cc-pVxZ, x = T, Q. A total of 7 structures for GaN2+ and 24 for GaN4+ were identified, corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces, and bonding mechanisms for some low-lying electronic states. The calculated dissociation energy (De) of the ground state of GaN2+, X1Sigma+, is 5.6 kcal/mol with respect to Ga+(1S) + N2(X1Sigmag+) and that of the excited state, ã3Pi, is 24.8 kcal/mol with respect to Ga+(3P) + N2(X1Sigmag+). The ground state and the first excited minimum of GaN4+ are of 1A1(C2v) and 3B1(C2v) symmetry with corresponding De of 11.0 and 43.7 kcal/mol with respect to Ga+(1S) + 2N2(X1Sigmag+) for X1A1 and Ga+(3P) + 2N2(X1Sigmag+) for 3B1.