An Ab Initio Journey toward the Molecular-Level Understanding and Predictability of Subnanometric Metal Clusters

Current advances in synthesizing and characterizing atomically precise monodisperse metal clusters (AMCs) at the subnanometer scale have opened up new possibilities in quantum materials research. Their quantizied “molecule-like” electronic structure showcases unique stability, and physical and chemical properties differentiate them from larger nanoparticles. When integrated into inorganic materials that interact with the environment and sunlight, AMCs serve to enhance their (photo)catalytic activity and optoelectronic properties. Their tiny size makes AMCs isolated in the gas phase amenable to atom-scale modeling using either density functional theory (DFT) or methods at a high level of ab initio theory, even addressing nonadiabatic (e.g., Jahn–Teller) effects. Surface-supported AMCs can be routinely modeled using DFT, enabling long real-time molecular dynamics simulations. Their optical properties can also be addressed using time-dependent DFT or reduced density matrix (RDM) theory. These theoretical–computational efforts aim to achieve predictability and molecular-level understanding of the stability and properties of AMCs as function of their composition, size, and structural fluxionality in different thermodynamical conditions (temperature and pressure). In this perspective, the potential of ab initio and DFT-based modeling is illustrated through recent studies of unsupported and surface-supported AMCs. Future directions of research are also discussed, including applications and methodological enhancements beyond the state-of-the-art.