First-principles molecular-dynamics simulations of a hydrous silica melt: Hydrogen diffusion mechanisms and electronic properties

摘要

We study a sample of liquid silica containing 3.84 wt.% H_2O with 06 initio molecular dynamics simulation in its liquid state at temperatures of 3000 K and 3500 K. At these temperatures the liquid can be brought into equilibrium after several picoseconds. Hence we are able to investigate possible diffusion mechanisms for hydrogen atoms. It turns out that intermediate states in the liquid play a decisive role for the diffusion of hydrogen. Quenches of selected configurations to ambient temperature allow us to study the electronic structure of the material. In particular we find electronic states in the band gap of amorphous silica. The correlation of these electronic states with the structural intermediate states that are present in our system and which we make responsible for the hydrogen diffusion has already been discussed for a long time.