Grégory Geneste, Marc Torrent, François Bottin, Paul Loubeyre
The role of quantum nuclear zero-point motion in the structural changes of solids H2 and D2 under pressure is investigated at 80 K up to 160 GPa by first-principles path-integral molecular dynamics calculations. A radical revision of the current interpretation of the nature of phase II is presented. An isotope difference for the structure of phase II is discovered. Phase II of solid D2 is identical to the classical counterpart (C2/c space group). Phase II of solid H2, exhibits large and very asymmetric angular quantum fluctuations. The quantum-mechanically averaged structure (close to Cmcm), is different from the most probable one (Cmc21). That fits the concept of "quantum fluxional solid", which cannot be understood in terms of a single classical structure. The mechanism of the transition into phase III is also obtained. Existing structural data support this microscopic interpretation.
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http://arxiv.org/abs/1205.2290
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