Structural, Vibrational, and Electronic Properties of Copper-Doped Silicon and Germanium Cation Clusters Cu<i>X</i>_<i>n</i>⁺ (X = Si or Ge, <i>n</i> = 6–16): A Density Functional Theory Study

The incorporation of transitional elements into silicon or germanium-based semiconductor clusters not only notably improves their structural stability but also endows them with unprecedented multifunctionalities. In this work, the structural, vibrational, and electronic properties for copper-doped silicon and germanium cation clusters Cu<i>X</i> _<i>n</i> ⁺ (X = Si or Ge, <i>n</i> = 6-16) are systematically investigated. The ground-state structures are identified using the PBE0 and mPW2PLYP method combined with a global search technique. The structure evolutions of CuSi <i>_n</i> ⁺ and CuGe <i>_n</i> ⁺ are both from adsorption to endohedral configurations. The transfer point for CuGe <i>_n</i> ⁺ is at <i>n</i> = 9 earlier than CuSi <i>_n</i> ⁺ at <i>n</i> = 12 due to the larger ionic radius of Ge compared to Si, which was further proven by the consistency between the simulated and the available experimental infrared spectra. Through comparative analysis of average binding energies and bond lengths, it is found that CuSi <i>_n</i> ⁺ exhibits higher stability than CuGe <i>_n</i> ⁺ of the same size. According to calculation results, the CuGe₁₀ ⁺ cluster has excellent stability, high structure symmetry, a proper HOMO-LUMO gap, and a wide absorption band in the visible light range, making it a potential candidate for semiconductor nanomaterials and photodetector applications.