Structure, electronic properties and electronic excitation analyses of Si60[sbnd]Si60 dimer and Si59Al[sbnd]Si59P complex

Abstract

The electronic properties of nanoclusters, such as Si60 cage, are remarkably changed by substitution of heteroatom such as Al or P. How do such impure Si60 cages behave when brought together to form a complex? To address this, we have performed DFT and TD-DFT based calculations on Si60Si60 dimer and Si59AlSi59P complex. We have explored various electronic properties of Si59AlSi59P complex and compared with those of Si60Si60 dimer. We notice that the bonding along with binding energies of cages in the complex is slightly different than that of dimer. The higher dipole moment and smaller energy gap of the complex compared to dimer suggest its increased polarity and conductivity. The density-of-state curves reveal that the frontier orbitals of the complex are slightly shifted relative to dimer such that their energy gap is decreased. The electronic excitation analyses suggest that the electronic transition in Si59AlSi59P complex takes place via charge transfer (CT) mode, and the strength of this CT interaction is much larger than that of Si60Si60 dimer. This is confirmed by larger oscillator strength, larger distance between the centroid of hole and electron as well as larger Δr index value. We believe that these findings might be useful in the application of Si-nanoclusters in the field of molecular electronics and nanoelectronics.