Structures of 1,4,6,9,11,14,16,19-tetraoxacycloeicodane (THF-based 16-crown-4 derivative, ionophore 1), its derivatives, and the derivative-cation (Li+, Na+, K+, and H+) complexes have been optimized using ab initio Hartree-Fock (HF) and single point second-order Moller-Plesset (MP2) methods. The geometric structures of ionophore 1, h-tetraMe-ionophore, and v-tetraMe-ionophore are optimized to macrocyclic cages with C-4 symmetry. Four oxygen atoms which are the binding sites of the cage are located at the bottom of the ionophore derivative. The cavity sizes of the derivatives are expanded by the symmetric substitution of the methyl groups. The symmetrically expanded derivatives can easily capture the cations to go through the cavity. In ionophore-M+ complexes, M+ is coordinated with four oxygen atoms of the derivatives and located at the center. Li+ is disposed in the plane of the cyclic frame. The van der Waals radius of Li+ fits well with the cavity size of the derivatives. While, the van der Waals radii of Na+ and K+ are larger than the cavity size, Na+ and K+ are disposed on the lower side of the mean plane of the cyclic frames. Meanwhile, in ionophore-H+ complexes, H+ is optimized to be bridged between two neighboring oxygen atoms. As the ionic size increases, the distances (R-OO) between two opposite oxygen atoms as welt as the distances (R-OM) between a cation and the oxygen atoms also increase. The atomic charges of Li+ are less positive than those of the other cations, and the charges of the oxygens are more negative than those of the carbon atoms. The ratio of the (atomic charge/ionic radius) of Li+ converges to 1. The binding energies from Li+ to K+ decrease monotonically.