Electronic structure calculations using the BPW91, B3LYP, MP2, and CCSD(T) approximations, in conjunction with the 6-311+G(2df) basis set, have been performed to obtain optimized geometries and energies of the low-lying states of AlO4 and AlO4-. At the CCSD(T) level, the (2)A(2) (C-2v) dioxo-superoxide is at least 0.5 eV lower in energy than both the (2)A(2) (D-2d) and B-2(1) (C-2v) isomers earlier predicted for the ground state. The calculations find a (1)A(1) (D-2d) ground state for AlO4-. The anion is stable toward electron detachment with vertical electron detachment energy of 4.65 eV and adiabatic electron detachment energy of 4.37 eV. (C) 2009 Elsevier B.V. All rights reserved.