In this study, hydroxycalix[4]arene, hydroxycalix[5]arene, hydroxycalix[6]arene, and their complexes with uranyl and thorium ions were analyzed by density functional theory. The coordination ability of hydroxycalixarene ligands to uranyl and thorium ions could be analyzed by simulating the infrared and ultraviolet–visible spectra, the Wiberg bond energy levels, the energy gaps, and the binding energies. We found that various hydroxycalixarene complexes with uranyl or thorium ions had significant differences in their properties, as well as in t...