The electronic structure of GaP3- and GaP3 is investigated using density functional theory (B3LYP-DFT), second-order Moller-Plesset perturbation theory (MP2) and the coupled cluster [CCSD(T)] approximation in conjunction with the 6-311+G(2dt) one particle basis set. The ground state of GaP3- is computed to be (2)A' with a C-s geometry. Vertical electron detachment energies of the anion are reported and three of the bands observed in the GaP3- photodetachment spectrum are reassigned. The ground state of GaP3 is computed to be (1)A'-C-s with a (1)A(1)-C-2v state within 0.3 eV above. The adiabatic electron affinity (AEA) of GaP3 is calculated to be 1.84 eV at the CCSD(T)//B3LYP and CCSD(T)//MP2 levels. (C) 2004 Published by Elsevier B.V.