Electronic structure investigation of the Al4O4 molecule

Structural properties of energetically low-lying isomers of the isolated Al4O4 molecular system have been investigated by theoretical ab initio techniques within the Hartree–Fock (HF) and second-order Møller–Plesset (MP2) frozen core level of approximation and density functional methods (DFT) employing the Becke-3–Perdew-86 (B3P86) hybrid functional. In total, nine local minima representing six Al4O4 isomers of various spin multiplicities are completely characterised. The two energetically lowest of these stationary points, a singlet of planar D2h and a triplet of cubic Td symmetry, are furthermore sifted by considering other choices of exchange (B, B3) and correlation (LYP, PW91) functionals as well as higher levels of theory (G2/MP2, G2, and CCSD(T), D2h only). We report energies, equilibrium geometric parameters, selected harmonic vibrational wavenumbers along with corresponding absorption coefficients and compare the different computational approaches.