Molecular dynamic simulation amorphous ices

When partially hydrated samples are cooled down to 77 K, no crystallization peak is detected by differential thermal analysis. The x-ray and neutrons show that an amorphous form is obtained and its structure is different from those of low-and high-density amorphous ices already known [5]. Samples with lower levels of hydration corresponding to one monolayer coverage of water molecules are under investigation. This phenomenon looks similar in both hydrophilic and hydrophobic model systems. However, in order to characterize more precisely the nature of the amorphous phase, the site-site partial correlation functions need to be experimentally obtained and compared with those deduced from molecular dynamic simulations. 

It is well known that irradiation alters the structure of ice. It is amorphized at T < 80 K by protons, ions, photons and electrons. The structures of the irradiated ices have only been determined in the case of intense electron irradiation, where the high-density amorph was detected. Recent molecular dynamic simulations have also shown a densification of the ASW ice when irradiated with 35 eV water molecules,but these simulations also questioned the existence of the high-density phase as the initial structure of ice films deposited at low temperature. 

For an example of the enhancement in sputter yields resulting from large cluster ion impact, see Table 3.2. This lists sputter yields of H2O molecules from a 500-nm film of amorphous ice deposited on a Silver substrate resulting from Au, AU2, Au3 , and Cgo ion impact at 40° with respect to the sample normal as defined via Molecular Dynamics simulations (Szakal et al. 2006). 

TABLE 3.2 Sputter Yields of HjO Molecules as Determined by Molecular Dynamics Simulations from a 500-nm Film of Amorphous Ice on Silver Resulting from the Listed Projectiles all Incident at 40° (Szakal et al. 2006). 

M. Seidl, T. Loerting and G. Zifferer. High density amorphous ice Molecular dynamics simulations of the glass transition at 0.3 GPa. J. Chem. Phys. 131, 2009,114502-1-7. 

M. Seidl, T. Lxjerting and G. Zifferer. Molecular dynamics simulations on the gjass-to-liquid transition in high density amorphous ice. Z. Phys. Chem. 223, 2009,1047-1062. 

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