Modelling the structural evolution, electronic structures and optical properties of Sc6Sen0/- (n = 1–12) clusters

The size-dependent structural evolution of scandium–selenium cluster remains poorly understood, particularly regarding the origin of growth transitions and the emergence of stable building blocks. Here, neutral and anionic Sc6Sen0/- (n = 1–12) clusters were systematically investigated by global search techniques combined with B3LYP density functional theory calculations, with additional single-point validation at the B3LYP-D3(BJ) and DLPNO-CCSD(T) levels. The results reveal a clear two-stage growth behavior with n = 8 as the critical turning point. For n = 1–8, Se atoms sequentially occupy the eight electrostatic potential minima sites on the Sc6 octahedral core, ultimately forming the highly symmetric Chevrel-phase Sc6Se8 cluster. This transition point is governed by both geometric and electronic factors. As a result, the clusters undergo structural reorganization for n = 9–12, giving rise to competing link-like and pentagonal-pyramidal motifs. Stability analyses based on average binding energy and second-order energy difference identify Sc6Se8 as the most distinguished cluster in the series. Simulated photoelectron, vibrational, and ultraviolet–visible spectra provide characteristic fingerprints for structural identification. In particular, Sc6Se8 exhibits pronounced aromaticity, strong visible-light absorption, and favorable excitonic features, highlighting its role as a magic super-atomic building block in the Sc–Se system. The size-dependent structural evolution of scandium–selenium clusters remains poorly understood, particularly regarding the origin of growth transitions and the emergence of stable building blocks. Here, the authors combine global search techniques, density functional theory calculations and additional single-point validation to study neutral and anionic Sc6Sen0/- (n = 1–12) clusters, reporting a two-stage growth behavior with n = 8 as the critical turning point, after which structural reorganization leads to competing link-like and pentagonal-pyramidal motifs.