Theoretical study of the physical properties of binary Si mC n ( [formula omitted]) clusters: An ab initio study

Abstract

An ab initio study of the structural, electronic, optical and vibrational properties of small silicon-carbon binary nanoclusters Si m C n ( m + n ⩽ 5 ) has been made. We use a self-consistent pseudopotential method within the static and the time-dependent density functional theory (TDDFT). We optimize fully 27 structures. The structural parameters, binding energies (BE's), highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps, charge accumulation on atoms, dipole moment, optical spectra and the vibrational frequencies have been computed. The clusters containing the maximum number of C–C and/or Si–C bonds are found to be relatively more stable. The most stable structures are those containing a comparatively large number of carbon atoms. It is observed that, in general, whenever the number of carbon atoms exceeds the number of silicon atoms the most stable structures are seen to be either linear or planer. On the other hand, when the Si atoms are nearly equal to or greater than C-atoms, the stable structures are found to be three-dimensional ones. The clusters containing even number of carbon atoms are much stronger than those clusters containing odd number of carbon atoms. Computed values of different Si–Si, Si–C and C–C bond lengths are in very good agreement with the available experimental data. Also, the calculated vibrational frequencies for different clusters are in reasonable agreement with the available experimental values. The growth of these most stable structures should be possible in the experiments. The absorption is seen in the near and far ultraviolet region.