Keynote: CMST 2018

2018 ◽  
Vol 1 (1) ◽  
pp. IX
Author(s):  
Miroslava Aleksandrova Nedyalkova
Keyword(s):  
Surface Charge ◽  
Water Distribution ◽  
Water Molecules ◽  
Salt Solutions ◽  
Interaction Sites ◽  
Surface Sites ◽  
Nanoparticle Surface ◽  
Monovalent Ions ◽  
Dynamics Simulations ◽  
Added Salt

Molecular dynamics simulations were performed to study the ion and water distribution around a spherical charged nanoparticle (Fig.1). A soft nanoparticle model was designed using a set of hydrophobic interaction sites distributed in six concentric spherical layers. To simulate the effect of charged functionalized groups on the nanoparticle surface, a set of charged sites were distributed in the outer layer. Four charged nanoparticle models, from a surface charge value of −0.035 C m−2 to −0.28 C m−2 were studied in NaCl and CaCl2 salt solutions at 1 M and 0.1 M concentrations to evaluate the effect of the surface charge, counterion valence, and concentration of added salt. We obtain that Na+ and Ca+2 ions enter inside the soft nanoparticle. Monovalent ions are more accumulated inside the nanoparticle surface, whereas divalent ions are more accumulated just in the plane of the nanoparticle surface sites. The increasing of the salt concentration has little effect on the internalization of counterions, but significantly reduces the number of water molecules that enter inside the nanoparticle. The manner of distributing the surface charge in the nanoparticle (uniformly over all surface sites or discretely over a limited set of randomly selected sites) considerably affects the distribution of counterions in the proximities of the nanoparticle surface.rphological changes.

Molecular Dynamics Simulations of Water and Ion Structures Near Charged Surfaces

2007 ◽  
Author(s):  
Dongyan Xu ◽  
Deyu Li ◽  
Yongsheng Leng
Keyword(s):  
Molecular Dynamics ◽  
Surface Charge ◽  
Molecular Dynamics Simulations ◽  
Single Molecule ◽  
Research Field ◽  
Water Molecules ◽  
Wall Region ◽  
Surface Charges ◽  
Ion Distribution ◽  
Dynamics Simulations

Extensive research has been devoted to nanofluidics in the past decade because of its potential applications in single molecule sensing and manipulations. Fundamental studies have attracted significant attention in this research field since the success of nanofluidic devices depends on a thorough understanding of the fluidic, ionic, and molecular behavior in highly confined nano-environments. In this paper, we report on molecular dynamics simulations of the effect of surface charge densities on the ion distribution and the water density profile close to a charged surface. We demonstrate that surface charges not only interact with mobile ions in the electrolyte, but also interact with water molecules due to their polarizability, and hence influence the orientation of water molecules in the near wall region. For the first time, we show that as the surface charge density increases, the water molecules within ∼ 5 Å of the {100} silicon surface will evolve from one layer into two layers. Meanwhile, the orientation of the water molecules is more aligned instead of randomly distributed. This layering effect may have important implications on electroosmotic flow through nanochannels and heat transfer across the solid-liquid interface.

The Effects of Ions and Surface Charge Density on Water Distribution in Silicon Nanochannel

2012 ◽  
Author(s):  
Yinghua Qiu ◽  
Qiyan Tan ◽  
Weichuan Guo ◽  
Yunfei Chen
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Charge Density ◽  
Water Distribution ◽  
Pure Water ◽  
Water System ◽  
Water Layer ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Nacl Solution

Water distributions are obtained in the silicon nanochannels filled with NaCl solution and pure water with molecular dynamics simulation, respectively. Taking into account the reality at the solid-liquid interface, the silicon atoms of channel walls in the model are allowed to vibrate at their own equilibrium positions. Results show that: The water distribution vertical to the channel wall changes notably due to the introduction of Na+ ions and Cl− ions. In pure water case, there are three water aggregation peaks within 0.4nm from surface, in contrast to two in NaCl solution case. Also, the locations and values of the corresponding peaks alter except the first one. However, the water distribution for NaCl solution beyond 0.5nm shares the same trend with that in pure water and the water molecules alignments in the first layer have almost the same trend in the two cases. Furthermore, in pure water system, the influence range of surface charge is 0.55nm and with surface charge density increasing, the first concentration peak changes into three ones within 0.4nm perpendicular to the surface and the water molecules in the first water layer align more orderly.

An Investigation of the Structure of Aqueous Electrolyte Solutions by Statistical Geometry

1993 ◽  
Vol 48 (7) ◽  
pp. 806-810 ◽  
Author(s):  
M. Kiselev ◽  
M. Poxleitner ◽  
J. Seitz-Beywl ◽  
K. Heinzinger
Keyword(s):  
Aqueous Electrolyte ◽  
Quantitative Description ◽  
Electrolyte Solutions ◽  
Water Molecules ◽  
Statistical Geometry ◽  
Monovalent Ions ◽  
Definition Of ◽  
Dynamics Simulations ◽  
New Criterion ◽  
Structure Breaking

Abstract Statistical geometry is employed for a quantitative description of deviations from regular octahedrality of water around monovalent ions and from regular tetrahedrality of solvent water around water molecules. For these deviations a new criterion is presented by taking into account octahedral and tetrahedral spatial symmetry groups. A geometrical definition of structure making and structure breaking is proposed and illustrated on the basis of molecular dynamics simulations of 2.2 molal aqueous KCl and LiI solutions with the flexible BJH model of water.

scholarly journals Electrical Breakdown Mechanism of Transformer Oil with Water Impurity: Molecular Dynamics Simulations and First-Principles Calculations

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 123
Author(s):  
Bin Cao ◽  
Ji-Wei Dong ◽  
Ming-He Chi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Diffusion ◽  
First Principles ◽  
Electrical Breakdown ◽  
Transformer Oil ◽  
Water Molecules ◽  
Conducting Channel ◽  
Breakdown Mechanism ◽  
Water Impurity ◽  
Dynamics Simulations

Water impurity is the essential factor of reducing the insulation performance of transformer oil, which directly determines the operating safety and life of a transformer. Molecular dynamics simulations and first-principles electronic-structure calculations are employed to study the diffusion behavior of water molecules and the electrical breakdown mechanism of transformer oil containing water impurities. The molecular dynamics of an oil-water micro-system model demonstrates that the increase of aging acid concentration will exponentially expedite thermal diffusion of water molecules. Density of states (DOS) for a local region model of transformer oil containing water molecules indicates that water molecules can introduce unoccupied localized electron-states with energy levels close to the conduction band minimum of transformer oil, which makes water molecules capable of capturing electrons and transforming them into water ions during thermal diffusion. Subsequently, under a high electric field, water ions collide and impact on oil molecules to break the molecular chain of transformer oil, engendering carbonized components that introduce a conduction electronic-band in the band-gap of oil molecules as a manifestation of forming a conductive region in transformer oil. The conduction channel composed of carbonized components will be eventually formed, connecting two electrodes, with the carbonized components developing rapidly under the impact of water ions, based on which a large number of electron carriers will be produced similar to “avalanche” discharge, leading to an electrical breakdown of transformer oil insulation. The water impurity in oil, as the key factor for forming the carbonized conducting channel, initiates the electric breakdown process of transformer oil, which is dominated by thermal diffusion of water molecules. The increase of aging acid concentration will significantly promote the thermal diffusion of water impurities and the formation of an initial conducting channel, accounting for the degradation in dielectric strength of insulating oil containing water impurities after long-term operation of the transformer.

scholarly journals Origin and control of ionic hydration patterns in nanopores

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Miraslau L. Barabash ◽  
William A. T. Gibby ◽  
Carlo Guardiani ◽  
Alex Smolyanitsky ◽  
Dmitry G. Luchinsky ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Distribution Functions ◽  
Water Molecules ◽  
Surrounding Water ◽  
Ionic Hydration ◽  
Hydration Shells ◽  
Water Layers ◽  
Dynamics Simulations ◽  
And Control

AbstractIn order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

scholarly journals Optimal Relabeling of Water Molecules and Single-Molecule Entropy Estimation

Biophysica ◽  
2021 ◽  
Vol 1 (3) ◽  
pp. 279-296
Author(s):  
Federico Fogolari ◽  
Gennaro Esposito
Keyword(s):  
Single Molecule ◽  
Degrees Of Freedom ◽  
Water Molecules ◽  
Maximum Information ◽  
Nearest Neighbours ◽  
Biomolecular Simulations ◽  
Solvent Molecules ◽  
Solvation Entropy ◽  
Dynamics Simulations ◽  
Internal Degrees Of Freedom

Estimation of solvent entropy from equilibrium molecular dynamics simulations is a long-standing problem in statistical mechanics. In recent years, methods that estimate entropy using k-th nearest neighbours (kNN) have been applied to internal degrees of freedom in biomolecular simulations, and for the rigorous computation of positional-orientational entropy of one and two molecules. The mutual information expansion (MIE) and the maximum information spanning tree (MIST) methods were proposed and used to deal with a large number of non-independent degrees of freedom, providing estimates or bounds on the global entropy, thus complementing the kNN method. The application of the combination of such methods to solvent molecules appears problematic because of the indistinguishability of molecules and of their symmetric parts. All indistiguishable molecules span the same global conformational volume, making application of MIE and MIST methods difficult. Here, we address the problem of indistinguishability by relabeling water molecules in such a way that each water molecule spans only a local region throughout the simulation. Then, we work out approximations and show how to compute the single-molecule entropy for the system of relabeled molecules. The results suggest that relabeling water molecules is promising for computation of solvation entropy.

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