From Aromatic Motifs to Cluster-Assembled Materials: Silicon-Lithium Nanoclusters for Hydrogen Storage Applications.

Silicon-lithium clusters are promising candidates for hydrogen storage due to their lightweight composition, high gravimetric capacities, and favorable non-covalent binding characteristics. In this study, we employ density functional theory (DFT), global optimization (AUTOMATON and Kick-MEP), and Born-Oppenheimer molecular dynamics (BOMD) simulations to evaluate the structural stability and hydrogen storage performance of key Li-Si systems. The exploration of their potential energy surface (PES) reveals that the true global minima of LiSi and LiSi differ markedly from those of the earlier Si-Li structures proposed as structural analogs of aromatic hydrocarbons such as benzene and naphthalene. Instead, these clusters adopt compact geometries composed of one or two Si () units and a Si dimer, all stabilized by surrounding Li atoms. Motivated by the recurrence of the Si- motif, we explore oligomers of LiSi, which can be viewed as electronically transmuted analogues of P, confirming the additive H uptake across dimer, trimer, and tetramer assemblies. Within the series of Si-Li clusters evaluated, the LiSi sandwich complex, featuring a σ-aromatic Si ring encapsulated by two Li moieties, achieves the highest hydrogen capacity, adsorbing 34 H molecules with a gravimetric density of 23.45 wt%. Its enhanced performance arises from the high density of accessible Li adsorption sites and the electronic stabilization afforded by delocalized σ-bonding. BOMD simulations at 300 and 400 K confirm their dynamic stability and reversible storage behavior, while analysis of the interaction regions confirms that hydrogen adsorption proceeds via weak, dispersion-driven physisorption. These findings clarify the structure-property relationships in Si-Li clusters and provide a basis for designing modular, lightweight, and thermally stable hydrogen storage materials.