Theoretical study on Raman radial breathing vibration of SiO₂ nanostructures

Using the B3LYP method based on the density functional theory, a quasi-1D SiO2 nanochain formed by SiO2 2MR, and the Raman vibration spectra of a SiO2 nanotube composed of 3MR, 4MR, 6MR and 8MR were calculated at 6-31G(d) level. Through the analysis of Raman spectra, it is found that Raman radial breathing vibration frequency of the nanochain and nanotube moves to the opposite direction with the increase of their length, namely, the red shift and blue shift turn up. However, Raman frequencies trend to reach the different stable values with the approximation of the infinite frequency, and the vibration frequencies reduce with the diameter increase of the nanochain and nanotube. Due to the internal structure stress of nanomaterial, the frequency shift is more obvious for small size material. The further analysis of bond length and bond angle of all kinds of structures shows that the function of the structure stress causes the frequency drift according to the size of the nanomaterial.