Role of disorder in incorporation energies of oxygen atoms in amorphous silica - art. no. 224207

We investigate the role of static disorder on defect energetics on examples of interstitial oxygen atoms in amorphous (a)-SiO2. We generate representa tive amorphous structures using molecular dynamics with empirical potential s and refine them using the periodic plane-wave density-functional method ( DFT). We calculate the DFT distribution of incorporation energies for 96 pe roxy-linkage (PL) configurations in a periodic model of a-SiO2. The calcula tions show a big site-to-site variation of incorporation energies. We parti tion the oxygen atom incorporation energy into contributions from a small l ocal cluster around the defect and from the rest of the amorphous network. The striking result is that the incorporation of a defect can create as wel l as release the strain energy in the embedding network. The variation of t he PL incorporation energy is dominated by the contribution from the surrou nding amorphous network, with the distortion of the local geometry of the d efect contributing only about one third of the total variation. The two con tributions are statistically independent. Our results provide an analysis o f the distribution of defect incorporation energies in a-SiO2 and emphasize the importance of disorder and statistical approaches, which cannot be ach ieved in crystalline and cluster models of amorphous structure. Additionall y, since the defect energies can be so strongly dependent on the longer-ran ge strain fields, amorphous samples prepared differently and hence having d ifferent distributions of strain may perform differently in applications.