Structural evolution, electronic structures, and optical properties of W3Sn (n = 1-12) clusters: A density functional theory study.

Tungsten incorporation provides an effective strategy for regulating the structural stability and electronic and optical properties of sulfur clusters. Herein, the structural evolution, electronic structures, vibrational spectra, relative stabilities, and optical properties of neutral W3Sn (n = 1-12) clusters were systematically investigated by using global search techniques combined with density functional theory calculations. The results reveal a distinct three-stage growth pattern. In the first stage (n = 1-4), S atoms are sequentially adsorbed at the WW edge-bridging sites of the W3 triangular unit, followed by central capping to form an incomplete cubane-type W3S4 structure. In the second stage (n = 5-7), the W3S4 core is preserved, and additional S atoms are attached to W sites to generate terminal sulfido groups. In the final stage (n = 8-12), further sulfur incorporation leads to sulfur saturated structures containing S2 and S3 units while retaining the triangular W3 core. Simulated IR and Raman spectra show a systematic blue shift of the characteristic peaks, reflecting the evolution from WS stretching to more diverse WS and SS vibrational modes. Stability analyses identify W3S6 as the most stable cluster, with the highest average binding energy and fragmentation energy. The calculated HOMO-LUMO gaps of W3Sn clusters fall within the semiconductor range, and W3S6 exhibits broad visible-to-near-infrared absorption dominated by HOMO-to-LUMO type transitions. Further analyses reveal that the stability and optical activity of W3S6 arise from strong WS orbital hybridization, polar covalent bonding, and mixed localized and charge-transfer excitation characteristics, highlighting its potential for semiconductor and optoelectronic applications.