Temperature-induced topological differentiation of the two high-density amorphous icesA. M. Saitta, Th. Strässle and S. Klotz
Physique des Milieux Denses, Institut de Minéralogie et Physique des Milieux Condensés CNRS-UMR 7590, Université Pierre et Marie Curie - F-75252 Paris, France
received 17 January 2006; accepted in final form 7 March 2006
published online 5 April 2006
The high-density (HDA) and the very high-density (VHDA) amorphous forms of ice are studied through computer simulations. The structural transformations involve, at different stages of compression, two different subgroups of second-shell neighbors. The interplay between these subgroups is found to be crucial in the mechanism of high-pressure differentiation between HDA and VHDA: in HDA they are more separated and the first subgroup is locked in the anti-tetrahedral, ice-VII-like positions all along the downstroke to ambient pressure. In VHDA the annealing under pressure triggers instead the merging of the two subgroups through a counter-intuitive outward displacement of one subgroup of neighbors, resulting then in a local decrease of the coordination number, a more random-close-packed arrangement and a different equation of state.
61.43.-j - Disordered solids.
61.43.Bn - Structural modeling: serial-addition models, computer simulation.
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