Rigid unit modes in the molecular dynamics simulation of quartz and the incommensurate phase transition |
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| Authors: | Frank Stefan Tautz Volker Heine Martin T Dove Xiaojie Chen |
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| Institution: | 1. Cavendish Laboratory, University of Cambridge, Madingley Road, CB3 OHE, Cambridge, UK
2. Department of Earth Sciences, University of Cambridge, Downing Street, CB2 3EQ, Cambride, UK
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| Abstract: | A molecular dynamics simulation of quartz at different temperatures both in the a and in the  phase has been conducted. The  - phase transition could be observed. A phonon analysis of the -phase confirms and rounds out in a quantitative way the origin of the incommensurate (ic) modulated phase. In particular it traces the optic soft mode at  becoming (to a good approximation) a so-called rigid unit mode (RUM) at q 0, and elucidates its coupling to the transverse acoustic mode which precipitates the incommensurate transition. This success underpins and illuminates the concept of RUMs and their role in structural phase transitions. |
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