Beyond activity coefficients with pairwise interacting surface (COSMO-type) models

Pairwise interacting surface models, like COSMO-RS and COSMO-SAC, are getting popular in the prediction of activity coefficients when experimental data is scarce. In this work an alternative derivation of the COSMO -SAC model is presented and pair contact probabilities as well as nonrandom factors are compared with classic models. By using these probabilities one can readily calculate the system internal energy (or enthalpy). The case of temperature dependent interaction energies and the potential inconsistencies in this case are discussed in detail. Many properties of the resulting equations are discussed, including the issue of distinguishable or indistinguishable segment types. An accompanying open-source code favoring readability over efficiency is also provided.

Automated summary

This paper presents an alternative derivation of the COSMO-SAC model and compares pair contact probabilities as well as nonrandom factors with classic models. By using these probabilities, the system internal energy can be readily calculated. The case of temperature dependent interaction energies and potential inconsistencies are discussed, and an accompanying open-source code is provided, favoring readability over efficiency.