Molecular dynamics studies of self-interstitials in ice Ih

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Abstract
We carried out molecular dynamics simulations of interstitial water molecules in ice to clarify behavior and vibrational properties of self‐interstitials in ice. We used an atom–atom potential model developed by Kumagai et al. [N. Kumagai, K. Kawamura and T. Yokokawa, Mol. Sim. 12, 177 (1994)] which allows intramolecular motions. We confirmed high reliability of the potential model for reproducing the structure and vibrational spectra of ice. From trajectory observations of self‐interstitials, we found that a stable interstitial site is an uncapped trigonal site. By comparing power spectra of vibrational motions for self‐interstitials with that of matrix ice, we found that the large formation entropy of the interstitial molecule is attributed to much higher density of states in a low frequency region for the interstitial than that for the matrix.