Molecular dynamics computation of the dynamical structure factor of a Lennard–Jones glass: Propagation of acoustic modes at the nm-scale

The collective vibrational atomic dynamics of metallic glasses is a longstanding subject of debate. The origin of the excess of vibrational modes known as the Boson peak is not clear, though it appears to be connected to the so-called quasi-localized eigen-modes of the vibrational spectrum. However, it has not yet been shown if this is an universal phenomenon affecting all classes of glasses. Computation of the dynamical structure factor by molecular dynamics (MD) may allow us to analyse the factors influencing the features of the Boson peak. Here we report a procedure to compute the vibrational density of states (VDOS), which was used to analyse the vibrational spectrum of Lennard–Jones glasses. Via the current–current correlation function, we obtain the dynamic structure factor. In order to reach the momentum values accessible experimentally, MD simulations must be performed in large enough boxes. Furthermore, the atomic dynamics must be recorded for times long enough so as to gain access to the experimental energy spectrum regime, thus implying a large computational effort. Results of this simulation will be compared to those obtained via exact diagonalization methods reported by Derlet et al. [Eur. J. Phys. B 85 (2012) 148] as well as to experimental data from Inelastic Scattering.

► Acoustic excitations with nm-scale wavelengths studied by molecular dynamics.
► Binary Lennard–Jones system compared to experimental behaviour of metallic glasses.
► Boson peak anomalies originated by atoms in low shear modulus zones.
► Nanometric mechanical heterogeneities effects on Boson peak frequency region.