Simulation of Two-level Tunneling States and Floppy Modes in Silica Glass

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We present the results of a computational study of the low-energy dynamics of silica glass. Molecular dynamics simulation results show that parts of the glass structure can undergo large cooperative reorientations of SiO4 tetrahedra. These motions involve reorientations of about 30 tetrahedra with an energy barrier of about 0.06 eV. We relate these motions to the presence of double-well potentials which give risetotwo-level tunneling states, thereby providing the mechanism for the anomalous low-temperature thermal properties of glasses. In addition to studying the exibility of silica glass in terms of the large tetrahedral rearrangements, we also address the exibility of silica glass in terms of its ability to sustain Rigid Unit Modes, or modes that propagate without distortion of SiO4 tetrahedra. We found that silica glass is surprisingly similar to its corresponding crystalline phases in its ability to support RUMs. We relate this similarity is related to the structural similarity of silica glass and its crystalline phase over short length scales.

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Journal: TechConnect Briefs
Volume: 2, Technical Proceedings of the 2001 International Conference on Computational Nanoscience and Nanotechnology
Published: March 19, 2001
Pages: 121 - 124
Industry sector: Advanced Materials & Manufacturing
Topic: Informatics, Modeling & Simulation
ISBN: 0-9708275-3-9