A Helical Monolayer Ice

Gao

et al. 2020

J. Phys. Chem. Lett.

Although computational prediction of new ice phases is a niche field in water science, the scientific subject itself is representative of two important areas in physical chemistry, namely, statistical thermodynamics and molecular simulations. The prediction of a variety of novel ice phases has also attracted general public interest since the 1980s. In particular, the prediction of low-dimensional ice phases has gained momentum since the confirmation of a number of low-dimensional “computer ice” phases in the laboratory over the past decade. In this Perspective, the research advancements in computational prediction of novel ice phases over the past few years are reviewed. Particular attention is placed on new ice phases whose physical properties or dimensional structures are distinctly different from conventional bulk ices. Specific topics include the (i) formation of superionic ices, (ii) electrofreezing of water under high pressure and in a high external electric field, (iii) prediction of low-density porous ice at strongly negative pressure, (iv) ab initio computational study of two-dimensional (2D) ice under nanoscale confinement, and (v) 2D ices formed on a solid surface near ambient temperature without nanoscale confinement. Clearly, the formation of most of these novel ice phases demands certain extreme conditions. Ongoing challenges and new opportunities for predicting new ice phases from either classical molecular dynamics simulation or high-level ab initio computation are discussed.

mentioning

confidence: 99%

Computational Prediction of Novel Ice Phases: A Perspective

Gao

et al. 2020

J. Phys. Chem. Lett.

Physica Status Solidi (b)

“…We are ready to define the global quantum discord (GQD). [17][18][19][20][21][22][23][24] Let's consider an m-site system, whose state is described by a density matrix ρ ½1...m , and the reduced density matrix of site j is denoted as ρ j ½ with j ¼ 1; . .…”

Section: Global Quantum Discordmentioning

confidence: 99%

Global Quantum Discord in Transverse‐Field Ising Models on N × N Square Lattices

Sun

Zhou

Wang

et al. 2019

Global quantum discord (GQD) in two‐dimensional (2D) transverse‐field Ising models on N × N square lattices at zero temperature and finite temperatures are studied. First, the GQD Gtrue(ρ2×2true) defined on the reduced density matrix ρ2×2 of a 2 × 2 sub‐square in the center of the N × N lattices, with N=4, 5, 6, 7, ∞ is studied. It is found that Gtrue(ρ2×2true) shows little size dependence in the strong‐field and weak‐field limit, and presents dramatic size dependence in the middle‐field region. The results are explained by short‐range correlations in non‐critical regions and long‐range correlations in critical regions of the models, respectively. Then the scaling behavior of the GQD Gtrue(true|ψg〉true) of the ground states for the entire N × N squares is studied. It is found that Gtrue(true|ψg〉true) contains a 1D contribution (corresponding to the side length of the squares) and a 2D contribution (corresponding to the area of the squares). Furthermore, the effect of thermodynamic fluctuations on GQD by investigating the thermal‐state GQD Gtrue(e−HkBTtrue) is considered. In high‐temperature regions, GQD is always destroyed by thermodynamic fluctuations for any strength of the magnetic field. However, in low‐temperature regions, some thermal enhancement of GQD under weak fields and some thermal robustness of GQD under strong fields is observed. The results are explained by the low‐lying energy states and the energy gap of the models.

“…Interfaces between solids and water are ubiquitous in nature and are responsible for many physical phenomena, including wetting on surface [1][2][3], electrochemical corrosions [4][5][6] and electrodeposition [7][8][9]. Thus, the interaction between water and solid surfaces have been extensively studied [10], with aims to identify exotic water structuring at the interface [11][12][13][14], achieve high-performance energy storage devices [15][16][17] and develop new principles for water energy harvesting [18][19][20][21][22][23]. Water-solid interactions are often dominated by the socalled electric double layer (EDL) formed at solid-liquid interfaces [20,21,[24][25][26], composed of an ion layer firmly adsorbed on the solid surface, called the Stern layer, and a layer of counter-ions in water attracted to the Stern layer, called the diffusion layer.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic insight into electricity generation from moving ionic droplets on graphene

Zhang

Guo

2021

Sci. China Mater.

Self Cite

Recent experiments have demonstrated that moving water droplets on polymer-supported graphene can generate electric voltages in graphene. Here, we perform a multi-scale analysis on the mechanism of the generated voltages on the basis of an interplay among the substrate, graphene and ionic water. We find that the attraction of ions in water by substrate dipoles drives charge redistribution in graphene, forming an electric triple layer (ETL) at the water/ graphene/substrate interface, made of an ion layer fixed on graphene, an image charge layer in graphene and a counterion layer in water. As a droplet moves on graphene, dynamic formation of the ETL at its front end drives a flow of charge in graphene. Using Langmuir adsorption theory combined with ab initio calculations, we determine the ion concentration in the ETL and estimate the amount of charge that each ion can draw in graphene. Then, the electric current in graphene is formulated in terms of ion concentration, droplet velocity, graphene thickness and density of substrate dipoles, which well reproduces experimentally measured currents in graphene. These results underscore the importance of tailoring substrate dipoles in optimizing the performance of devices for water energy harvesting and promoting practical applications.