COSMO-RS

COSMO-RS (short for COnductor like Screening MOdel for Real Solvents)[1][2][3] is a quantum chemistry based equilibrium thermodynamics method with the purpose of predicting chemical potentials μ in liquids.

It processes the screening charge density σ on the surface of molecules to calculate the chemical potential μ of each species in solution.

As an initial step a quantum chemical COSMO[4] calculation for all molecules is performed and the results (e.g. the screening charge density) are stored in a database.

In a separate step COSMO-RS uses the stored COSMO results to calculate the chemical potential of the molecules in a liquid solvent or mixture.

As long as the above assumptions hold, the chemical potential μ in solution can be calculated from the interaction energies of pairwise surface contacts.

In the Ehb expression σacc and σdon are the screening charge densities of the hydrogen bond acceptor and donor respectively.

The max[] and min[] construction ensures that the screening charge densities of the acceptor and donor exceeds the threshold for hydrogen bonding.

All parameters either are general or element specific, which is a distinctive feature of COSMO-RS as compared to group contribution methods like UNIFAC.