A first principles study of noble metal-doped silicon nanocrystals Si$_{n-1}$M (n = 75 and 150 and M = Cu, Ag, Au)

Silicon nano-structures can have important roles in many useful applications, such as in nano-scale energy conversion materials, as nano-detectors of gas particles or as thermoelectric materials. To achieve efficient performance of these nano-devices, electronically tailored nano-materials are needed. For this a thorough understanding of both doped and undoped nano-structures is essential. Here we will present results of our first principles spin polarized electronic structure calculations of noble metal atom doped silicon nanocrystals using a hybrid density functional theory method (B3LYP-DFT) and a LanL2DZ basis set. The nanocrystals are used here as a test group, and are based on three different isomers of bulk silicon: diamond, wurtzite, and BC8. Geometry optimizations of the pure Si$_{n}$ nanocrystals were performed for spin magnetic moments of s=0 \textit{$\mu $}$_{B}$ and s=2 \textit{$\mu $}$_{B}$ for each isomer. Then the substitutional doping of M atom was done separately at the inside and at the surface of the nanocrystals. The doped nanocrystals' geometries were also optimized for spin magnetic moments s=1 \textit{$\mu $}$_{B}$ and s=3 \textit{$\mu $}$_{B}$. For the bigger nanocrystals, the energy differences between the two spin states are very small. Binding energies and HOMO-LUMO gaps were calculated and a comparative analysis of the pure and doped silicon nanocrystals will be presented.