Vibrational density of states of TiO2 nanoparticles

• Vibrational Density Of States of rutile and amorphous TiO2 nanoparticles are reported.
• VDOS extends in low and high frequency range for rutile and amorphous TiO2 nanoparticle.
• Ti contributes to low frequency range while O contributes to entire frequency range.
• VDOS of amorphous phase nanoparticles can be well represented by the step function.

The lattice dynamics (LD) and molecular dynamics (MD) simulations are carried out to investigate the phonon dispersion relations of rutile supercell and vibrational density of states (VDOS) of 3 nm size rutile and amorphous TiO2 nanoparticles using the Matsui and Akaogi (MA) rigid ion model. The calculated phonon dispersion relations and optical mode frequencies at symmetry points agree evenly with the experimental data except in the low frequency range. The VDOS of rutile and amorphous nanoparticles get extended in the 0–2 THz and in the 24–32 THz frequency range as compared to bulk VDOS due to structural changes in the core and surface regions of rutile and amorphous nanoparticles. The Ti atom's contribution to VDOS is in the range of acoustic and low frequency optical modes while the O atom's contribution is significant in the entire frequency range due to mass and number differences. The VDOS of amorphous phase nanoparticles can be well represented by the step function to study the thermodynamical properties of nano phase TiO2 and may be a model for future experiments.