Markgraf, JanJanMarkgrafLisboa Girardi, D. G.D. G.Lisboa GirardiSmirnova, IrinaIrinaSmirnovaMüller, SimonSimonMüller2026-09-042026-09-042026-07-24Fluid Phase Equilibria 612 (C): 114820 (2026)https://hdl.handle.net/11420/64625The COSMO-SAC-Phi model developed by Soares et al. extends the COSMO-SAC activity-coefficient framework into a full equation of state by explicitly accounting for pressure effects. In this approach, pure substances and mixtures are represented as pseudo-mixtures consisting of the actual number of moles and an additional pseudo-component that describes free volume, or holes. In this work, we implement this extension within the openCOSMO-RS framework and evaluate it using a large and diverse set of molecules and binary systems. The resulting equation of state includes an extensive open-source parameter set with around 1800 pure-component entries, made freely available to the academic community. The four pure-component parameters were fitted to vapor-pressure and liquid-molar volume data for each substance. Model performance was assessed against two benchmark equation-of-state databases, one for pure compounds and one for binary mixtures, without introducing any binary interaction parameters. The resulting openCOSMO-RS-Phi model reproduces the accuracy of the original COSMO-SAC-Phi formulation while providing a fully open-source and accessible implementation for the scientific community. Beyond its immediate utility, it also establishes a foundation for future development of predictive EoS for electrolyte solutions.en0378-38122026CElsevierhttps://creativecommons.org/licenses/by/4.0/COSMO-RSOpen-sourceParameterizationORCAEquation of StateTechnology::660: Chemistry; Chemical EngineeringNatural Sciences and Mathematics::540: ChemistryJournal Article2026-09-0310.1016/j.fluid.2026.11482010.15480/882.1819210.1016/j.fluid.2026.114820