Study of structures, energies and vibrational frequencies of (O2)n+ (n = 2–5) clusters by GGA and meta-GGA density functional methods

Using Generalized Gradient Approximation (GGA) and meta-GGA density functional methods, structures, binding energies and harmonic vibrational frequencies for the clusters O4+, O6+, O8+ and O10+ have been calculated. The stable structures of O4+, O6+, O8+ and O10+ have point groups D2h, D3h, D4h and D5h optimized on the quartet, sextet, octet and dectet potential energy surfaces, respectively. Rectangular (D2h) O4+ has been found to be more stable compared to trans-planar (C2h) on the quartet potential energy surface. Cyclic structure (D3h) of O6+ cluster ion has been calculated to be more stable than other structures. Binding energy (B.E.) of the cyclic O6+ is in good agreement with experimental measurement. The zero-point corrected B.E. of O8+ with D4h symmetry on the octet potential energy surface and zero-point corrected B.E. of O10+ with D5h symmetry on the dectet potential energy surface are also in good agreement with experimental values. The B.E. value for O4+ is close to the experimental value when single point energy is calculated by Brueckner coupled-cluster method, BD(T).