Relativistic density functional investigation of the mono-lanthanum silicide clusters LaSin (n=1-6): geometries, electronic properties and IR spectra

The mono-lanthanum silicide clusters LaSin (n=1-6) have been studied adopting the relativistic density functional calculation with generalized gradient approximation. Considering different spin configurations, we calculated and discussed the equilibrium geometries, charge populations, the HOMO-LUMO gaps, as well as infrared (IR) absorption spectra of LaSin (n=1-6) clusters. It is found that: the lowest-lying LaSin (n=1-6) clusters basically maintain a similar framework to the low-lying Sin+1 clusters, and the La atoms prefer the surface sites. The relative stabilities are investigated based on the calculation of fragmentation energies and, showing that LaSi2, LaSi4, and LaSi5 clusters have enhanced stabilities. Charge populations analysis shows that the charges transfer from La atom to Sin framework and the La atom acts as an electron donor. HOMO-LUMO gaps indicate that LaSi2 and LaSi5 clusters have higher chemical stabilities. IR absorption spectrum and vibrational mode analysis show that the highest frequency absorption peaks all correspond to the breathing mode of the silicon framework, and the characteristic infrared absorption peaks caused by La atom vibration, except for LaSi dimer, all appeared in the low-frequency region.