Cohesive energy density is an important property in solvents that is typically used to have a quick idea on whether substances have affinity for each other. Usually, roughly speaking, molecules with high cohesive energy density go well with other molecules with high energy density, and vice-versa. Not only COSMO-RS can predict equilibrium thermodynamics properties of/in liquids such as vapor pressure, boiling point, VLE/LLE or partition coefficients, COSMO-RS can also provide an estimate for this basic descriptor of substances.

The advantage of cohesive energy density as a descriptor is that it can be calculated once for a substance and then stored, and easily re-used. This underpins the well-known Hansen Solubility parameters. It turns out that the Mixture panel in COSMOtherm provides a descriptor called "H_int" which quantifies the amount of energy a molecule in a defined medium, as well as Volume which is the volume (averaged over the conformers) occupied by the cavity inside the COSMO surface. H_int/V is the cohesive energy density.

To get this descriptor for a list of molecules:

1- load the list of molecules in the software
2- click the Mixture panel
3- click "Add All pure"
4- once the output appears, click "Show extended output"
5- export the content to a speadsheet of your choice
6- divide the column H_int (kcal/mol) by Volume (in Angstroms^3) and change units as desired. This provides a prediction for cohesive energy density that can then be used to evaluate "at a glance", for example, which solvent would be best in a given list to dissolve a given solute.

What is your favorite new feature of the 2023 release?