Physics Theory Seminar with Robert Wexler on Surface Phase Diagrams from Nested Sampling

Atomic-scale modeling of surface phase equilibria at finite temperatures has always been challenging due to the complexity of surface configurational space and, therefore, the difficulty in computing the free energy of surfaces. In this proof-of-concept work, we predict coverage-temperature surface phase diagrams and identify phase transitions of adsorbates on both flat and stepped facets of the face-centered cubic Lennard-Jones solid. These phase transitions typically feature an enthalpy-driven condensation at higher temperatures and an entropy-driven reordering process at lower temperatures. We capture both energetic and entropic (including translational, rotational, anharmonic vibrational, and configurational) contributions to the surface phase transitions with nested sampling. Overall, we demonstrate the ability and potential of nested sampling for predicting the structure of hard-to-measure in situ surfaces, e.g., that govern the activity and selectivity of heterogeneous catalysts.