Geometrical stabilities and electronic properties of Si-n (n=12-20) clusters with rare earth holmium impurity: a density functional investigation

HoSin (n = 12-20) clusters with different spin states have been systematically investigated by using density functional theory with the generalized gradient approximation. The total energies, growth-pattern and equilibrium geometries as well as the APT charges of the HoSin (n = 12-20) clusters are calculated. The relative stabilities in terms of the calculated atomic averaged binding energies and fragmentation energies are discussed, revealing that the cake-like HoSin (n = 16, 18, 20) clusters have enhanced stabilities. Furthermore, the highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO) gaps of the HoSin (n = 12-17) are above 1.55 eV while HoSi16 has the largest one (1.95 eV). Interestingly, the calculated dipole moments of the cake-like HoSin (n = 16, 18, 20) clusters are very small, corresponding to the global minima. According to the calculated APT charges of the Ho atom in the HoSin (n = 12-20) clusters, the contribution of charge-transfer to the stability of HoSin clusters is briefly discussed, manifesting that the charges in HoSin clusters transfer from the Si atoms to the Ho atom. Additionally, the optimized geometries show that the rare earth Ho atom is completely encapsulated into the centre of the Si frame at n = 15. This finding is in good agreement with the available experimental results.