Low-frequency atomic motion in a model glass

A molecular-dynamics simulation is presented which explores the microscopic dynamics of a monatomic model glass. The investigated systems consist of up to 32000 atoms interacting via a Lennard-Jones potential. The normal-modes analysis has been used to determine the pattern of atomic displacements. Except for the highest frequencies, all the vibrational modes are found to be delocalized. In the lowest-frequency region the pattern of atomic displacements associated with a given eigenmode is composed by an uncorrelated random component plus well-defined sinusoidal-like waves. The two components are of comparable amplitudes.