Updated united-atom force field for organophosphorus compounds

Organophosphorus compounds are widely used as extractants in solvent extraction for metal recovery. Accurate molecular simulations of these systems are, however, hindered by the limited performance of general-purpose force fields. In this study, we present an updated version of the GROMOS united-atom force field tailored for this chemical class. Lennard-Jones parameters for phosphoryl groups were revised based on literature data, and charge derivation strategies evaluated. A set of 28 representative molecules, including key extractants such as TBP, Cyanex 272, and D2EHPA, were simulated by molecular dynamics to assess density, viscosity, and enthalpy of vaporization. The revised force field with scaled (0.89×) and RESP charges significantly improved the accuracy of property predictions, reaching errors within chemical accuracy. This provides a reliable basis for simulating complex multiphase systems relevant to metal extraction and recycling.