Optimized geometries and vibrational frequencies are calculated for Ca+-X and Y-Ca+-X complexes (X, Y = H2O, N-2, CO2, O-2, and O), required for understanding the chemistry of calcium in the upper atmosphere. Both MP2 and B3LYP optimizations were performed employing 6-311 +G(2d,p) basis sets. In some cases a number of different orientations had to be investigated in order to determine the one of lowest energy, and in cases involving O and O-2, different spin states also had to be considered. In order to establish accurate energetics, RCCSD(T) single-point energy calculations were also employed, using aug-cc-pVQZ basis sets. Accurate dissociation energies for the Ca+-X and X-Ca+-Y species are derived and discussed. Comparison with available experimental results is made where possible.