科研之友
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摘要
Electronic and spectral properties of small TiO2 particles have been studied in order to gain more knowledge on their dependence on the crystal- and particle-size distributions. Our goal is to extend the recently developed light scattering based method for determining submicrometer size particles to nanoparticles. For that, we need to know how the refractive index function depends on the cluster size. As a first step, we have used time-dependent density functional theory (TDDFT) calculations having a focus on the shape changes of the calculated spectra, which can be related to changes in the refractive index function. Starting from the structure of TiO2 molecule for the two smallest particles and truncated bulk anatase structure for larger particles, the structures for (TiO2)(n) clusters, n = {1, 2, 8, 18, 28, 38}, have been modeled. After the structure optimization using standard density functional theory (DFT) approach, the photoabsorption spectra for the optimized particle structures have been calculated by using TDDFT calculations. The results show slight evidence of the band gap broadening in the case of three out of the smallest particles and strong structural dependence of electronic and spectral properties, which can partly be related to the transformation of the electron structure, and breaking of the crystal symmetry as the size of the particle becomes smaller. These findings indicate that in the case of small particles their refractive index function can differ from the bulk values, and this has to be taken into account in the interpretation of light-scattering measurements.
- 出版日期2011-5-5
