Asymmetric Twinned-FCC Configuration Alone Cannot Effectively Induce Metallicity in ∼200-Atom Gold Nanoclusters: Design and Theoretical Study of Tetrahedral Au₄-Cored RS-AuNCs

This study proposes a novel design strategy for thiolate-protected gold nanoclusters (RS-AuNCs) based on the truncated triangular Au₁₂ unit on the [111] crystal plane. First, sandwich-type primary cores of Au₂₄, Au₂₅, and Au₂₆ are constructed on the Au₁₂ crystal plane, and then triangular Au₃ units are introduced to obtain core structures of Au₂₇, Au₂₈, and Au₂₉, respectively. Finally, based on the Au₂₉ core, four asymmetric twinned-FCC shell clusters (Au₁₉₇(SR)₆₆, Au₂₀₀(SR)₆₆, Au₂₀₃(SR)₆₉, and Au₂₀₆(SR)₇₂) are successfully constructed through differentiated ligand protection modes. Calculations of average formation energy (<i>E</i>_ave) and atomization energy (<i>E</i>_atomization) demonstrate exceptional structural stability in these clusters. Electronic structure analyses reveal their extremely narrow orbital energy gaps, while the absence of SPR peaks and limited electronic spatial extent (⟨<i>r</i>²⟩) confirm their nonmetallic nature. This work provides the first elucidation that asymmetric twinned-FCC structures cannot induce metallic characteristics, uncovering a synergistic regulation mechanism of cluster electronic states by multiple parameters including Au atom count, stacking configuration, and core symmetry. These findings offer new insights into structure-property relationships of RS-AuNCs and provide significant guidance for the precision design of functional metal nanomaterials.