Vibrational dynamics and boson peak in a supercooled polydisperse liquid

Abraham, Sneha Elizabeth and Bagchi, Biman (2010) Vibrational dynamics and boson peak in a supercooled polydisperse liquid. In: Physical Review E - Statistical, Nonlinear and Soft Matter Physics, 81 (3). 031506-1-031506-10.

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Abstract

Vibrational density of states (VDOS) in a supercooled polydisperse liquid is computed by diagonalizing the Hessian matrix evaluated at the potential energy minima for systems with different values of polydispersity. An increase in polydispersity leads to an increase in the relative population of localized high-frequency modes. At low frequencies, the density of states shows an excess compared to the Debye squared-frequency law, which has been identified with the boson peak. The height of the boson peak increases with polydispersity and shows a rather narrow sensitivity to changes in temperature. While the modes comprising the boson peak appear to be largely delocalized, there is a sharp drop in the participation ratio of the modes that exist just below the boson peak indicative of the quasilocalized nature of the low-frequency vibrations. Study of the difference spectrum at two different polydispersity reveals that the increase in the height of boson peak is due to a population shift from modes with frequencies above the maximum in the VDOS to that below the maximum, indicating an increase in the fraction of the unstable modes in the system. The latter is further supported by the facilitation of the observed dynamics by polydispersity. Since the strength of the liquid increases with polydispersity, the present result provides an evidence that the intensity of boson peak correlates positively with the strength of the liquid, as observed earlier in many experimental systems.

Item Type:	Journal Article
Publication:	Physical Review E - Statistical, Nonlinear and Soft Matter Physics
Publisher:	The American Physical Society
Additional Information:	Copyright of this article belongs to The American Physical Society.
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	09 Jun 2010 07:25
Last Modified:	23 Feb 2012 05:38
URI:	http://eprints.iisc.ac.in/id/eprint/27108

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