Pathways for the formation of ice polymorphs from water predicted by a metadynamics method

Abstract

pathways for the formation of ice polymorphs from water predicted by a metadynamics method Hiroki nada the mechanism of how ice crystal form has been extensively studied by many researchers but remains an open question. Molecular dynamics (MD) simulations are a useful tool for investigating the molecular-scale mechanism of crystal formation. However, the timescale of phenomena that can be analyzed by MD simulations is typically restricted to microseconds or less, which is far too short to explore ice crystal formation that occurs in real systems. in this study, a metadynamics (MtD) method was adopted to overcome this timescale limitation of MD simulations. An MD simulation combined with the MtD method, in which two discrete oxygen-oxygen radial distribution functions represented by Gaussian window functions were used as collective variables, successfully reproduced the formation of several different ice crystals when the Gaussian window functions were set at appropriate oxygenoxygen distances: cubic ice, stacking disordered ice consisting of cubic ice and hexagonal ice, highpressure ice Vii, layered ice with an ice Vii structure, and layered ice with an unknown structure. the free-energy landscape generated by the MtD method suggests that the formation of each ice crystal occurred via high-density water with a similar structure to the formed ice crystal. the present method can be used not only to study the mechanism of crystal formation but also to search for new crystals in real systems.

High-Density Liquid Water at a Water–Ice Interface

“…The revealed physical picture of the interface is analogous to the actively debated picture of nonclassical crystal growth, , which deviates from assumptions in classical crystal-growth theory, for example, in respect of the building units of a crystal incorporating into the crystal without any structural changes. In nonclassical growth, the building units in an ambient phase may adopt a conformation that is kinetically favorable and thermodynamically close to the crystalline phase before their incorporation into crystals.…”

The Local Vibrational Mode Theory and Its Place in the Vibrational Spectroscopy Arena

“…Relating our results to the currently accepted water-ice diagram (see Figure b) reveals that ices in the 0–0.7 GPa region are dominated by strong hydrogen bonds; ices in the central region (0.7–1.6 GPa) have a high percentage of intermediate hydrogen bonds whereas ices in the high-pressure region (up to 50 GPa) are mostly comprised of weak hydrogen bonds. Based on these findings we suggest using local mode force constants as a tool to predict at what pressure a new ice form will most likely be stable, guiding complex experiments aimed at verifying predicted ice forms; currently more than 50 …”

Collective Variables for Crystallization Simulations─from Early Developments to Recent Advances

“…Nada in 2020 proposed a method in which the radial distribution functions (RDFs) can be utilized as a CV for the formation of water polymorphs . They performed MetaD simulations using two CVs defined as two discrete oxygen–oxygen RDFs represented by Gaussian window functions.…”

“…Nada in 2020 proposed a method in which the radial distribution functions (RDFs) can be utilized as a CV for the formation of water polymorphs. 58 They performed MetaD simulations using two CVs defined as two discrete oxygen–oxygen RDFs represented by Gaussian window functions. Different polymorphs of ice such as cubic, stacking disorder 59 (consists of cubic and hexagonal), high pressure ice VII, layered ice with an ice VII, and layered ice with an unknown structure were identified from the MetaD simulation trajectory ( Figure 11 ).…”