Computational Modeling of a-SiO₂ Nanoparticles and their Electronic Structure Calculation
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The spherical amorphous silica (a-SiO₂) nanoparticles (NPs) are constructed from a previous continuous random network (CRN) model of a-SiO₂ with the periodic boundary. The models of radii 12 Å, 15 Å, 18 Å, 20 Å, 22 Å, 24 Å and 25 Å are built from the CRN structure. Then, three types of models are constructed. Type I has the surface dangling bonds not pacified. In type II models, the dangling bonds are pacified by hydrogen atoms. In type III models, the dangling bonds are pacified by the OH groups. These large models are used to perform the electronic structure calculation of NPs by using the orthogonalized linear combination of atomic orbital (OLCAO) method. The results show some trends in band gap variation for Type I models. The trends in band gap variation for other two types are less clear. A series of NP models with a spherical pore in the middle of a solid NP model are constructed and studied. Spherical pores of radii of 6 Å, 8 Å, 10 Å, 12 Å, 14 Å, 16 Å and 18 Å are introduced within the spherical model of radius 20 Å. After OLCAO calculation, it is found that the band gap values remain constant (5 eV) up to 21.6% porosity and then decreases with increased in porosity. The relation with thickness of the porous NP shell and the surface to volume ratio (S/V) with the calculated band gap are studied in the same manner and will be discussed.
Table of Contents
Introduction -- Theoretical background -- Method -- Results and discussion -- Conclusion and future work -- Appendix A. Abbreviations