Résumé:

Silica glass is a typical example of disordered material. Theoretically, molecular dynamics computer simulation is a common and effective way to investigate structural and dynamic microscopic properties of silica glass, such as pair correlation functions, bond angle distribution, vibrational density of states and so on. In this work, we have prepared several different silica models solely within the framework of first-principles approach of the order of hundred atoms (38 Si and 76 O atoms) and analyze their structural, electronic and vibrational properties. The SiO2 models have been generated by quenching liquid silica (equilibrated at 3600 K and with a density equal to 2.20 g/cm3 ) to room temperature (300 K) using different cooling rates. We have compared the microscopic properties with experimental and previous simulation results. We have found that the cooling rate affects the properties of generated silica samples and that the slowly quenched model gives better agreement with the experimental results. These models have been gradually compressed up to 2.67 g/cm3 density, which corresponds to about 7 GPa: just below the elastic to plastic transition regime (estimated around 8 to 10 GPa) of silica glass. To characterize microscopic properties of compressed silica models below the transition pressure is an important step to investigate the mechanism of the transition with further compressed silica models (above the transition pressure). We show the properties of these compressed silica models and compare them with those of the uncompressed ones. Another type of models are also generated by compressing and equilibrating the liquid silica at 3600 K to 2.67 g/cm3 and then quenched to 300 K. The microscopic properties of these samples will be also presented and discussed.