A theoretical study of CaC2 species and its cationic and anionic derivatives has been carried out. The predicted CaC2 global minimum is a T-shape singlet species of C-2v symmetry with a very high dipole moment, whereas the linear isomer is shown to be a transition state. The lowest-lying cyclic and linear triplet states lie about 18 and 38 kcal/mol, respectively, higher in energy than the ground state. Both CaC2+ and CaC2- have also T-shape global minima, and the lowest-lying linear states for these species are not true minima. (C) 2003 Elsevier B.V. All rights reserved.