Numerical study of the low-frequency atomic dynamics in a Lennard-Jones glass

We present a computer simulation study of a monatomic glass model. The investigated system consists of up to 32000 ‘argon’ atoms, interacting via a Lennard-Jones potential. Its dynamical properties have been investigated both by the time evolution of the atomic trajectories during molecular dynamics runs at low temperature and by the normal mode analysis (NMA) in the inherent configuration. In the NMA, we used both the direct diagonalization of the dynamical matrix and the spectral moment method. The vibrational density of states (DOS). the dynamic structure factors, the Raman spectrum and the spatial patterns of the eigenmodes have been calculated. The Raman spectrum shows the characteristic bump, that is the so-called ‘boson peak’, at frequencies where the DOS presents an excess of states with respect to the Debye behaviour. By the analysis of the previous dynamical quantities and from the direct inspection of the pattern of the eigenvectors, we derive a consistent picture of the atomic dynamics in the boson peak energy region.