Vibrations and Relaxations in a Soft Sphere Glass: Boson Peak and Structure Factors

Abstract

The dynamics of a soft sphere model glass, studied by molecular dynamics, is investigated. The vibrational density of states divided by ${\omega }^2$ shows a pronounced boson peak. Its shape is in agreement with the universal form derived for soft oscillators interacting with sound waves. The excess vibrations forming the boson peak have mainly transverse character. From the dynamic structure factor in the Brillouin regime pseudo dispersion curves are calculated. Whereas the longitudinal phonons are well defined up to the pseudo zone boundary the transverse ones rapidly get over-damped and go through the Ioffe-Regel limit near the boson peak frequency. In the high $q$ regime constant-$\omega$ scans of the dynamic structure factor for frequencies around the boson peak are clearly distinct from those for zone boundary frequencies. Above the Brillouin regime, the scans for the low frequency modes follow closely the static structure factor. This still holds after a deconvolution of the exact harmonic eigenmodes into local and extended m odes. Also the structure factor for local relaxations at finite temperatures resembles the static one. This semblance between the structure factors mirrors the collective motion of chain like structures in both low frequency vibrations and atomic hopping processes, observed in the earlier investigations.

References in corpus (3)

• Excess Modes in the Vibrational Spectrum of Disordered Systems and the Boson Peak
• Vibrations in glasses and Euclidean Random Matrix theory
• The crossover from propagating to strongly scattered acoustic modes of glasses observed in densified silica

Cited by in corpus (20)

• Vibrational instability, two-level systems and Boson peak in glasses
• Anomalous properties of the acoustic excitations in glasses on the mesoscopic length-scale
• The Ioffe-Regel criterion and diffusion of vibrations in random lattices
• Universal non-phononic density of states in 2D, 3D and 4D glasses
• Boson peak and Ioffe-Regel criterion in amorphous silicon-like materials: the effect of bond directionality
• Normal Modes in Model Jammed Systems in Three Dimensions
• Heat transport in model jammed solids
• Low-energy quasilocalized excitations in structural glasses
• Pressure dependence of the Boson peak in glasses
• Frustration-induced internal stresses are responsible for quasilocalized modes in structural glasses
• Universal disorder-induced broadening of phonon bands: from disordered lattices to glasses
• Neutron scattering study of the vibrations in vitreous silica and germania
• Disentangling boson peaks and Van Hove singularities in a model glass
• Density of states in random lattices with translational invariance
• Probing the role of mobility in the collective motion of non-equilibrium systems
• Stringlet Excitation Model of the Boson Peak
• An atomic mechanism for the boson peak in metallic glasses
• A thermodynamic treatment of the glass transition
• Thermal Conductivity of Glass-Forming Liquids
• Resonant Coupling and the Non-Phononic Flat Band in Amorphous Solids