Molecular dynamics simulation of the frequency spectrum of amorphous silica

The dynamic behavior of atoms in bulk amorphous silica SiO2 has been investigated by using the molecular dynamics computer simulation technique to generate the frequency spectrum. A modified Born–Mayer–Huggins equation was used as the interatomic potential function. Due to the covalency of the Si–O bond, the ability of using a central-force model to reproduce the short time atomic motion in SiO2 was evaluated. The frequency spectrum was generated from the Fourier transform of the velocity autocorrelation function and was compared with the experimentally obtained spectrum presented in the literature. Results show that the frequency spectrum generated here has the three major peaks which are characteristic of silica— i.e., peaks at ∼400, ∼800, and ∼1100 cm−1. Changes in the Si–Si or O–O repulsive parameters in the potential function can be used to alter the frequency spectrum. The 800 cm−1 peak, due to oxygen bending and Si motion, and the 150 cm−1 correlated motion peak are the most affected by the alteration of the repulsive parameters. The results indicate the adequacy of using the model and potential function used here to simulate the short time motion of atoms in amorphous silica.