Using density functional theory (B3LYP-DFT) and ab initio methods [MP2 and CCSD(T)] with the 6-311 +G(2df) one particle basis set, two singlet states ((1)A(1)-C-2v and (1)A'-C-s) are found to be nearly degenerate and lower in energy by at least 0.5 eV than the triplet ((3)A(2)-C-3v) state previously predicted as the ground electronic state of AlP3. AlP3- has an (2)A'-C-s ground state, with low-lying (2)A"-C-s,(2)A(1)-C-3v and (2)A(1)-C-2v excited states at 0.04, 0.25, 0.29 eV, respectively. The adiabatic electron affinity of AlP3 is calculated to be 1.9 eV. (C) 2002 Elsevier Science B.V. All rights reserved.