(265a) Adsorption Rates and Free Energies Calculations of Methanol-Pt(111) Under Liquid Solvent: Development and Assessment of an Interfacial Force Field

Accounting for solvent effects on the thermochemistry of liquid/metal interfaces—e.g., as employed in heterogeneous catalysis, electrochemistry, and biomedicine—is a grand challenge; however, characterization of solvent effects is thorny because of configurational disorder in the solvent structure. Our group previously developed a multiscale sampling strategies for simulating configurational influences to the diffusion and free energies of adsorbed species to solid surfaces under liquid solvent and showed that these method can reproduce exactly diffusion coefficient and the free energies calculated with empirically-based implicit solvation for systems that do not interact strongly with the liquid environment. For systems that do interact strongly with the liquid environment, our method serves as an improvement. However, our methods do not account for thermal fluctuations in the internal geometry of the surface species, which could influence both diffusion coefficient and free energies via conformational changes in the adsorbed species, which impact the local structure of liquid molecules. Herein, we investigate how conformational changes of adsorbate species influence diffusion and free energy. We developed a force field, named MePt-FF, that can capture chemical bonding between the catalytic species and the catalyst surface as well as thermal fluctuations of the catalytic species. MePt-FF can be used to model CH₃OH adsorption to Pt(111), as illustrate Figure 1a. To map the CH₃OH-Pt potential energy surface, we construct a set of 600 frames by dragging the CH₃OH to (Figure 1b) and over (Figure 1c) the Pt(111) surface. Partial optimizations of the CH₃OH are performed using the VASP code. Figure 1d shows a parity plot comparing the CH₃OH-Pt binding energy as computed with DFT and predicted with MePt-FF. We demonstrate the use of MePt-FF in calculating diffusion coefficient and free energy of CH₃OH under liquid solvent accounting solvent fluctuations and internal geometry of adsorbed CH₃OH.