Density functional theory (DFT) calculations are performed to study the Y4O molecule in its neutral, anionic, and cationic states. The equilibrium geometries of Y4O, Y4O-, and Y4O+ are trigonal bi-pyramids. The ground states of Y4O, Y4O-, and Y4O+ are triplet ((3)A(1)), doublet ((2)A"), and doublet ((2)A'), respectively. Time-dependent DFT is used to calculate the excited states. A theoretical assignment for the features in the experimental photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.