A Consistent Thermodynamic Characterization of the Adsorption Process through the Calculation of Free Energy Contributions

Weapply in this study different methodologies based on thermodynamicintegration (TI), free energy perturbation (FEP), and potential ofmean force (PMF) to address the challenging issue of the calculationof the free energy of adsorption. A model system composed of a solidsubstrate, an adsorbate, and solvent particles is specifically designedto reduce the dependence of our free energy results on the samplingof the phase space and the choice of the pathway. The reliabilityand efficiency of these alchemical free energy simulations are establishedthrough the closure of a thermodynamic cycle describing the adsorptionprocess in solution and in a vacuum. We complete this study by thecalculation of free energy contributions related to phenomena of desorptionof solvent molecules and desolvation of the adsorbate upon adsorption.This calculation relies on the work of adhesion, the interfacial tensionof the liquid-vapor of the solvent, and the free energy of solvationof the substrate. The different ways of calculating the free energyof adsorption are in excellent agreement and could complete experimentsin the field of adsorption by giving quantitative data on the differentenergy contributions involved in the process.