We examine the vibrational spectrum of a glass of soft spheres produced by quenching an equilibrated liquid (produced via constant-energy molecular-dynamics simulation) to zero temperature. Normal-mode analysis shows clearly the existence of (quasi)localized modes at the low-frequency end of the vibrational spectrum. The modes are found to be localized around atoms whose neighborhood structure differs significantly from the average glass environment. The effective masses of these modes range upwards from 10 atomic masses.
This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.66.636
Laird, Brian Bostian; Schober, H. R. (1991). "Localized low-frequency vibrational modes in a simple model glass." Physical Review Letters, 66(5):636-696. http://dx.doi.org/10.1103/PhysRevLett.66.636