(346bm) Prediction of Solvation Free Energies Using PC-SAFT Classical Density Functional Theory

The calculation of the solvation free energy (SFE) of complex solutes is an important task in technical and biological systems. The calculations are routinely performed with molecular dynamics (MD) or Monte Carlo simulations and the SFE is evaluated with off-the-shelf methods like BAR, MBAR and umbrella sampling. However, the estimation of the SFE is computationally expensive requiring large enough systems for suffient sampling of multiple points along the thermodynamic integration path. Classical density functional theory (DFT) reduces the computational cost but contains the full molecular fluid structure at the solute-fluid interface. Thus enabling the rapid sampling of large numbers of possible solute/solvent combinations. The previously published molecular density functional theory [1] is based on a six-dimensional solvent density and its free-energy functional is based on the homogeneous reference fluid approximation but requires the solvent‘s bulk direct correlation function as an input.

The PC-SAFT equation of state has succesfully been applied to inhomogeneous systems at solid-fluid interfaces [2] and the frameworks is expanded to study solvation in non-polar solvents. The predictive nature of the PC-SAFT equation of state allows the calculation of SFEs without any adjustable parameters or the prior knowledge of the solvent‘s direct correlation function.

Our works shows excellent agreement between the SFEs calculated by PC-SAFT DFT and MD simulations for a wide range of solute/solvent combinations in broad temperature and pressure windows. Furthermore, we calculate self-SFEs, i.e. residual chemical potentials, in different solvent mixtures and obtain very good results compared to the PC-SAFT equation of state. A current field of interest is the extension to polar solvents like alcohols and water.

[1]: Jeanmairet, G., Levesque, M., Vuilleumier, R., & Borgis, D. (2013). Molecular density functional theory of water. The journal of physical chemistry letters, 4(4), 619-624.

[2]: Sauer, E., Terzis, A., Theiss, M., Weigand, B., & Gross, J. (2018). Prediction of contact angles and density profiles of sessile droplets using classical density functional theory based on the PCP-SAFT equation of state. Langmuir, 34(42), 12519-12531.