The geometries，vibrational frequencies and bind energies are reported for the ground states of CaC2H2+ ，CaC2D2+and CaC2H4+ .CaC2H2^＋and CaC2H4^＋ equilibrium geometries have C2 symmetry with the metal ion lying in the perpendicular bisector of the C-C bond The ground state in both CaC2H2^＋ and CaC2H4^＋ molecules ia a^2 A state and the binding in the ground state is mainly electrostatic For both CaC2H2^＋ and CaC2H4^＋, the ligand is only slightly distorted from its free ligand structure．the C-C distance has hardly increased and there is only a very small bending of the H atom away from the Ca atom. This is consistent with the electrostatic natllfe of the bonding Two different approaches—Har~ree—Fock(HF)and density functional theory metbods(DFT) are used and basis Sets here used is 6-3ll+G(3df-2p) The DFT r~suhs are in good agreement witb experiments，namely，DFT methods provide the benefits that some more expensive ab initlo methods can do．but at essentially HF cost. So it is important to include electron correlation for accurate results in this study