Molecular dynamics analysis of elastic properties and new phase formation during amorphous ices transformations

Abstract

Unlike conventional first-order phase transitions, the kinetics of amorphous-amorphous transitions has been much less studied. The ultrasonic experiments on the transformations between low-density and high-density amorphous ice induced by pressure or heating provided the pressure and temperature dependencies of elastic moduli. In this article, we make an attempt to build a microscopic picture of these experimentally studied transformations using the molecular dynamics method with the TIP4P/Ice water model. We study carefully the dependence of the results of elastic constants calculations on the deformation rates. The system size effects are considered as well. The comparison with the experimental data enriches our understanding of the transitions observed. Our modeling gives new information about the formation mechanisms of new phase clusters during the transition between low-density and high-density amorphous ices. We analyse the applicability of the term “nucleation” for these processes.

Kinetics and Mechanisms of Pressure-Induced Ice Amorphization and Polyamorphic Transitions in a Machine-Learned Coarse-Grained Water Model

“…The transformation from LDA to HDA upon steadily increasing compression of ML-BOP happens through the appearance of multiple high-coordination clusters that grow gradually to form a high-density amorphous state (Figure b). The same has been observed in a recent simulation of pressure-induced transformation of LDA to HDA in TIP4P/Ice . Interestingly, we find that mW displays the same microscopic evolution from LDA to HDA upon compression as ML-BOP and TIP4P/Ice (Figure S4c).…”

“…We investigate the transformation between low- and high-density amorphous water by compression and expansion at 80 K and find it to occur sharply and reversibly, with significant hysteresis, similar to what has been reported in experiments . The sharp transition in density and local structure in the pressure-induced transformation of LDA to HDA is consistent with experimental observations and simulations using the all-atom ST2, TIP4P/2005, , and TIP4P/Ice water models that possess a liquid–liquid transition (LLT) at high pressure. , In contrast, we find that the mW model shows a gradual change in density and structure in the transformation of LDA to HDA and does not possess a LLT. , An assessment of our results along with previous results for all-atom models suggests that ML-BOP falls in the category of models that possess a LLT. Considering the similarities of the equations of state of ML-BOP and TIP4P/2005 in water’s stable, , metastable, , and glassy regimes, we expect the location of the LLCP of ML-BOP to be close to the one of TIP4P/2005, which is located at T c = 172 ± 1 K and P c = 186.1 ± 1 MPa …”

“…We investigate the transformation between low-and highdensity amorphous water by compression and expansion at 80 K and find it to occur sharply and reversibly, with significant hysteresis, similar to what has been reported in experiments. 37 The sharp transition in density and local structure in the pressure-induced transformation of LDA to HDA is consistent with experimental observations and simulations using the allatom ST2, 32 TIP4P/2005, 33,35 and TIP4P/Ice 44 water models that possess a liquid−liquid transition (LLT) at high pressure. 40,45 In contrast, we find that the mW model shows a gradual change in density and structure in the transformation of LDA to HDA and does not possess a LLT.…”

“…Molecular simulations with the TIP4P/Ice model indicate that the mechanism of transformation between HDA and LDA at 77 K with linearly increasing pressure occurs through formation of multiple clusters of the new phase at high level of metastability. , Likewise a simulation study of the HDA to LDA transformation upon isothermal decompression of TIP4P/Ice at temperatures from 170 to192 K, above T g and close to the estimated LLCP of the model, found spinodal-like nonequilibrium transformation between the two liquid phases. To date, the mechanism and kinetics of the LDA↔HDA transformations under isobaric–isothermal conditions have not been studied in simulations.…”

“…The same has been observed in a recent simulation of pressureinduced transformation of LDA to HDA in TIP4P/Ice. 44 Interestingly, we find that mW displays the same microscopic evolution from LDA to HDA upon compression as ML-BOP and TIP4P/Ice (Figure S4c). We conclude that the microscopic pathway from low-to high-density glasses upon compression cannot distinguish between models that have or lack a liquid−liquid transition.…”