The mole fraction of each compound of the solvent should be given with the subkey FRAC1 of the key COMPOUND for each compound. The solutes should have zero molar fraction in the solvent. It is possible to calculate the solubility of a solute at a temperature range, see key TEMPERATURE.
For solubility calculations of a solid compound one should add the pure compound melting point Tm, pure compound enthalpy of fusion ΔHfus, and optionally the pure compound heat capacity of fusion ΔCp using the subkeys meltingpoint, hfusion, and cpfusion, respectively, of the key COMPOUND for this compound. The COSMO-RS method does not predict these ΔHfus, ΔCp, or Tm.
The assumption made in the solubility calculation may be invalid in case of a solubility of a liquid in a solvent, especially if the solubility of the solvent in the liquid is high. For binary systems one may check this by calculating the miscibility gap in the binary mixture of the two liquids.
It is possible to calculate the solubility of a gas in a solvent, if one adds the subkey isobar and adds the partial vapor pressure partialvaporpressure (bar) of the gas as argument for the key PRESSURE:
PROPERTY solubility isobar End PRESSURE partialvaporpressure
The solubility of a gas in a solvent can also be calculated using Henry's law, which is valid for ideal dilute solutions, see see the key PROPERTY activitycoef.
The COSMO-RS calculation of the solubility of a compound is performed with an iterative method, since the activity coefficient of the compound depends on the molar fraction of this compound.