https://doi.org/10.1140/epjb/e2012-20902-0
Regular Article
The Boson peak of model glass systems and its relation to atomic structure
1
Condensed Matter Theory Group, Paul Scherrer
Institut, 5232
Villigen PSI,
Switzerland
2
Laboratory of Metal Physics and Technology, Department of
Materials, ETH
Zurich, 8093
Zurich,
Switzerland
a e-mail: peter.derlet@psi.ch
Received:
4
November
2011
Received in final form:
23
January
2012
Published online:
15
May
2012
Bulk metallic glasses (BMGs) exhibit a rich variety of vibrational properties resulting from significant atomic scale disorder. The Boson peak, which reflects an enhancement of states in the low frequency regime of the vibrational density of states (VDOS), is one such experimental signature of amorphous materials that has gained much interest in recent times. However, the precise nature of these low frequency modes and how they are influenced by local atomic structure remains unclear. Past simulation work has demonstrated that such modes consist of a mixture of propagating and localized components, and have been referred to as quasi-localized modes. Using standard harmonic analysis, the present work investigates the structural origin of such modes by diagonalising the Hessian of atomistic BMG structures derived from molecular dynamics simulations using a binary Lennard Jones pair potential. It is found that the quasi-localized vibrational modes responsible for the low frequency enhancement of the VDOS exist in a structural environment characterized primarily by low elastic shear moduli, but also increased free volume, a hydrostatic pressure that is tensile, and low bulk moduli. These findings are found to arise from the long-range attractive nature of the pair-wise interaction potential, which manifests itself in the corresponding Hessian as long-range off-diagonal disorder characterized by a distribution of negative effective spring constants.
Key words: Solid State and Materials
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2012