DFT modelling of fused silica electronic structure under strong laser-induced excitation

Abstract

Fused silica is an indispensable material in emergent photonic applications due to its unique optical, mechanical, and thermal properties, especially when it is nano-structured by an ultrashort laser pulse. The precision of the laser-induced modifications relies heavily on the control of the electron excitations and transient optical properties during the laser pulse. In this work we explore the fused silica band gap at high densities of excited electrons, using Density Functional Theory (DFT). Fused silica is a glass consisting of silica (SiO2) in amorphous form. It includes various structural variations since the topological arrangement of the SiO4 tetrahedra is not unique. We model fused silica as a molecule consisting of six SiO4 tetrahedra. Fused silica geometry parameters (bond lengths and angles) and electronic structure reported experimentally are well reproduced with a reasonable computational demand. Figure 1 shows the gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for molecular structures with different number of SiO4 tetrahedra. The HOMO-LUMO gap in this case represents the optical gap of fused silica measured experimentally.