Formation of Self-Trapped Holes in Silica From Density Functional Theory

Self-trapped holes (STHs) are defects formed in silica when holes couple with phonons and localize. They play a crucial role in understanding silica's interaction with light in applications such as scintillators and optical fibers. Ab-initio studies of STHs through DFT have been performed and benchmarked against experimental data, but they considered only the final polaron and not its formation process. Additionally, the results were sensitive to the fraction of exact exchange used. In this work, we compute the Eliashberg spectral function and electron-phonon matrix elements to provide a more detailed description of STH formation, and we use Koopman's theorem to tune the amount of exact exchange to include, correcting both deficiencies with earlier studies. Our approach enables us to rationalize why certain types of STHs, differentiated by their geometry, are available in amorphous vs crystalline silica. Furthermore, we find that the phonon modes most strongly coupled to the hole are those similar to the final lattice distortion in the polaron. Overall, our approach for more accurate description of STHs may enable the development of better devices as well as motivate future ab-initio exploration of STHs.