A study of the ground states of CaC_2H_2^+, CaC_2D_2^+ and CaC_2H_4^+

The geometries, vibrational frequencies and bind energies are reported for the ground states of CaC 2H + 2, CaC 2D + 2 and CaC 2H + 4. CaC 2H + 2 and CaC 2H + 4 equilibrium geometries have C 2v symmetry with the metal ion lying in the perpendicular bisector of the C-C bond. The ground state in both CaC 2H + 2 and CaC 2H + 4 molecules ia a 2A 1 state and the binding in the ground state is mainly electrostatic. For both CaC 2H + 2 and CaC 2H + 4 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 nature of the bonding. Two different approaches-Hartree-Fock(HF) and density functional theory methods(DFT)-are used and basis sets here used is 6-311+G(3df,2p). The DFT results are in good agreement with experiments, namely, DFT methods provide the benefits that some more expensive ab initio methods can do, but at essentially HF cost. So it is important to include electron correlation for accurate results in this study.