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This study investigates the finite-temperature behavior of phosphine-stabilized gold nanoclusters by integrating molecular dynamics simulations with Markov state models to analyze their free-energy landscapes and isomerization kinetics. The findings reveal that commonly reported crystal structures often represent minor metastable states rather than the dominant configurations at elevated temperatures, with increased ligand coverage significantly influencing thermodynamic and kinetic properties. Ultimately, the research underscores the necessity of considering these nanoclusters as dynamic ensembles, as their catalytically relevant geometries may be transient rather than stable states.
Crystal structures of gold nanoclusters often misrepresent their dominant finite-temperature states, revealing a dynamic ensemble that challenges traditional characterization methods.
Atomically precise phosphine-stabilized gold nanoclusters are commonly characterized by single-crystal X-ray diffraction, yet the extent to which these static structures represent finite-temperature behavior remains unclear. To explore the free-energy landscapes, equilibrium populations, and isomerization kinetics of these nanoclusters in the gas phase, we establish a general framework that combines molecular dynamics simulations based on a machine-learned interatomic potential with Markov state models (MSMs). Analysis of the MSMs indicates that experimentally reported crystal structures frequently correspond to minor metastable states or transient configurations rather than the dominant finite-temperature structures. Increasing ligand coverage systematically alters both the thermodynamics and kinetics of structural rearrangements, driving the transition from planar to three-dimensional gold cores while accelerating isomerization dynamics. Moreover, catalytically accessible geometries are often only minor members of the equilibrium ensemble, highlighting a trade-off between structural stability and surface accessibility. These results emphasize that ligand-protected nanoclusters need to be viewed as dynamic ensembles and their finite-temperature behavior cannot be fully captured by their corresponding crystallographic structures alone.
