The exact contribution of iodine-containing compounds is still not fully understood which is partially due to disagreements on the growth pathway. Previous studies, both computational and experimental, have suggested iodic and iodous acid pathways and iodine oxide pathways, however, a definitive conclusion is yet to be reached. Currently, very few relevant benchmark studies exist for iodine oxides such as iodine tetroxide (I 2 O 4 ) and iodine pentoxide (I 2 O 5 ). In addition, there are no actual benchmark studies of relevant iodine oxy-acids such as iodic and iodous acid, but some high-level calculations, CCSD(T)/CBS + spin-orbit coupling, have been carried out. Therefore, with the increasing number of computational studies on iodine-containing compounds, calculated with many differing methods (pure DFT, RI-CC2//DFT, and DLPNO-CCSD(T 0 )//DFT, all using pseudo-potentials for iodine), we find it important to benchmark a subset of the methods for the most atmospherically relevant iodine-containing compounds: iodous acid HIO 2 (IsA), iodic acid HIO 3 (IA), iodine tetroxide I 2 O 4 (IT), iodine pentoxide I 2 O 5 (IP). Here we benchmark methods for thermal energy contributions, single-point energy contributions, and spinorbit-coupling stabilization contributions. Spin-orbit-coupling was also benchmarked due to it having been shown to be relevant, especially for iodous acid. In addition to the benchmark we also present results for the binding free energy of dimers of IsA, IA, IT, and IP with water and various atmospherically relevant acids and bases: sulfuric acid (SA), methanesulfonic acid (MSA), nitric acid (NA), formic acid (FA), ammonia (AM), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). This work is the first in a series of papers that investigate the role of iodine species in atmospheric cluster formation.