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In this work, the dynamic behavior of nano-bubbles near the surface of single crystal iron (Fe) was investigated using molecular dynamics simulations. The cavitation erosion behavior of single crystal Fe and the structural evolution of its eroded surface was examined at different bubble diameters. The results show that nano-bubble diameter is inversely correlated with impact pressure and diameter is positively correlated with nanojet energy. The volume, surface area, and depth of cavitation pits are nearly directly proportional to the bubble diameter with correlation linear fitting coefficients of R2 = 0.9837, R2 = 0.9922, and R2 = 0.9799, respectively. Additionally, cavitation erosion induces the structural evolution of iron atoms from bcc to fcc and hcp structures. The percentage of new phase transformed is related to the bubble diameter and the type of transformed structure, the percentage of fcc and hcp structures of Fe atoms exhibits an increasing trend with the increase in the bubble diameter, and the Fe atoms of fcc structures occur an obvious increase beyond a bubble diameter of 12 nm. [ABSTRACT FROM AUTHOR]

In this work, the modified attachment energy model was used to predict the crystal morphology of isosorbide mononitrate (ISMN) in the dichloromethane (CH2Cl2) solvent system and dichloromethane-n-hexane (CH2Cl2-C6H14) mixed solvent system. The solvent effect can significantly affect the crystal morphology, which can profoundly impact both the drug's physicochemical properties and the subsequent technological treatment process. In addition, the interactions between solvent molecules and crystal faces were investigated using molecular dynamics simulation, and radial distribution function (RDF) analysis was performed to determine the types of interactions. The structural parameter S was introduced to characterize the roughness of each crystal surface; the change in the CH2Cl2 diffusion coefficient before and after the addition of C6H14 was analyzed using mean square displacement (MSD). The calculation results of the modified attachment energy from the two solvent systems revealed that C6H14 could accelerate crystal growth, while the crystal morphology was not greatly affected, which is of some significance as a guide for the industrial crystallization process. [ABSTRACT FROM AUTHOR]

The surface free energy of solids, γ, plays a crucial role in all physical and chemical processes involving material surfaces. For the first time, we obtained γ directly from molecular dynamics simulations using a crystal cleavage method. The approach was successfully realized in a Lennard-Jones system by inserting two movable external walls, each consisting of a single crystal layer, into a bulk crystal to create flat, defect-free surfaces. The cleavage technique designed allowed us to calculate the surface free energy according to its definition and avoid surface premelting. The temperature dependence of γ was determined for the (100) and (110) crystal planes along the whole sublimation line and its metastable extension, up to T = 1.02 · Tm, where Tm is the melting point. Good agreement with indirect values of γ(T) was found. The proposed computational cleavage method can be applied to other solids of interest, providing valuable insight into the understanding of chemical and physical surface processes, and demonstrates the successful import of the cleavage method, traditionally used in technical preparation and study of crystal surfaces, into a modern atomistic simulation. [ABSTRACT FROM AUTHOR]

A novel non‐phosphorus and non‐nitrogen scale inhibitor IA‐HEMA was synthesized in the presence of only C, H and O using itaconic acid (IA) and 2‐hydroxyethyl methacrylate (HEMA) as the raw materials and hydrogen peroxide‐ascorbic acid (H2O2‐ASA) as the initiating system. The synthesis conditions were optimized with the response surface method (RSM). The results indicated that the material ratio had the largest effect on the scale inhibition rate, followed by initiator dosage, polymerization temperature and polymerization time successively. As demonstrated by the static scale inhibition experiment, the scale inhibition rate was 97.27 % when the IA‐HEMA concentration was 100 mg/L. The mechanism was explored by molecular dynamics (MD). The results indicated that IA‐HEMA was able to overcome its own distortion and adsorb on the crystal surface, and the scale inhibition performance was related to its chelating and lattice‐distortion ability, which effectively inhibited the formation and precipitation of scale. All these findings suggest that IA‐HEMA is a quite promising environmentally friendly scale inhibitor in the salt system. [ABSTRACT FROM AUTHOR]

The molecular dynamics method is used to further reveal, from the molecular point of view, the mechanisms of salt inhibiting the hydration of Na-MMT. The interaction between water molecules, salt molecules, and montmorillonite are calculated by establishing the adsorption models. According to the simulation results, the adsorption conformation, interlayer concentration distribution, self-diffusion coefficient, ion hydration parameters, and other data are compared and analyzed. The simulation results show that the volume and basal spacing increase in a stepwise manner with the increase of water content, and water molecules have different hydration mechanisms. The addition of salt will enhance the hydration properties of compensating cations of montmorillonite and affect the mobility of particles. The addition of inorganic salts mainly reduces the adsorption tightness between water molecules and crystal surfaces, thereby reducing the thickness of water molecules layer, while the organic salts can better inhibit migration by controlling interlayer water molecules. The results of molecular dynamics simulations reveal the microscopic distribution of particles and the influence mechanism when the swelling properties of montmorillonite are modified by chemical reagents. [ABSTRACT FROM AUTHOR]

We develop a ReaxFF reactive force field used for the molecular dynamics simulations of thermophysical properties of liquid Cu and Zr metals. The ReaxFF parameters are optimized by fitting to the first-principles density-functional calculations on the equations of state for bulk crystal structures and surface energies. To validate the force field, we compare the ReaxFF results with those from experiments and embedded-atom-method (EAM) potentials. We demonstrate that the present ReaxFF force field well represents structural characteristics and diffusion behaviors of elemental Cu and Zr up to high-temperature liquid regions. It reasonably reproduces the thermodynamic processes associated with crystal-liquid interface. In particular, the equilibrium melting temperatures show better agreement with experimental measurements than the results from EAM potentials. The ReaxFF reactive force field method exhibits a good transferability to the nonreactive processes of liquid systems. [ABSTRACT FROM AUTHOR]

In this work, 3Mg(OH)2·MgCl2·8H2O (318MHCH) nanowires with ultra-high aspect ratios were first synthesized by a liquid method, and the effects of cetyltrimethylammonium bromide (CTAB) in highly concentrated salt solution were investigated. The structure and morphology of the synthesized 318MHCH nanowires were characterized. The as-prepared 318MHCH nanowires have a typical triclinic structure and relatively good crystallization properties. By introducing CTAB, the aspect ratio of 318MHCH nanowires will significantly increase from 500 to 4000. The high aspect ratio of 318MHCH nanowires is due to the increase in solution viscosity and the selective adsorption of CTAB molecules on the crystal surface. FTIR, Raman and XPS spectroscopy confirmed that the positively charged nitrogen-containing head of the CTAB molecule interacts with the surface of the 318MHCH crystal. Furthermore, since the (−1 0 1) plane has a lower electrostatic potential, the nitrogen-containing head of CTAB with a high potential is more readily adsorbed, which was confirmed by molecular dynamics simulations. Therefore, CTAB is selectively adsorbed on the side of 318MHCH nanowires, hindering the lateral growth and promoting the aspect ratio of 318MHCH nanowires. In addition, other cationic surfactants have been shown to have similar effects on the selective growth of nanowires. [ABSTRACT FROM AUTHOR]

How to effectively control the growth behavior of gypsum crystal in solution system has become one of the urgent problems to be solved in desulfurization industry, and the effective information of crystal growth process can' t be detected online timely and effectively. In this work, molecular dynamics simulation ( MS ) was used to calculate adhesion energy, face-center distance and area of specific plane of gypsum crystal, to determine morphologically dominant crystal planes and surface structure, and to theoretically study the interaction mechanism between sodium chloride and the main growth planes. The effect of sodium chloride on the crystal morphology of gypsum was obtained through experiments, which was compared with the results of MS. Results showed that sodium chlorides have varied effects on each crystal planes of gypsum crystals, which further changing the crystal morphology of gypsum. The simulation results are consistent with the experiment. MS can provide a theoretical support for morphology control of gypsum crystals. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have attracted significant interest as gas‐sensing materials due to their unique crystal structure and surface. However, there are still issues when it comes to expanding the types of sensing gases for the TMD gas sensors. To extend gas‐sensing selectivity for the TMD gas sensors in this study, a monolayer (ML) 2D metal–organic framework (MOF) is introduced on top of the PtSe2 gas sensor, thereby tuning the major sensing analyte of PtSe2 from NO2 to H2S. Density functional theory calculations elucidate that the metal species of ML MOFs are attributed to the tuned selectivity of the analytes, based on the difference in binding energies. It is also demonstrated that ML MOF maintained the high responsivity of the pristine PtSe2 even at a low concentration of gas (200 ppb). This is further confirmed through the molecular dynamics simulations, which reveal that the ML feature of the ML MOF is highly essential to preserve the intrinsic ultra‐low limit detection properties of pristine PtSe2. [ABSTRACT FROM AUTHOR]

Based on the modified embedded atom method (MEAM) potential suggested by Jin et al. (Appl. Phys. A120: 189, 2015), the molecular dynamics (MD) simulations were adopted to investigate the melting transition of the FCC transition metal Ni, and in the MD simulations, the forces acting on atoms were calculated by using the newly derived formulas. We first studied the melting points of Ni samples with low-index surfaces including Ni(100), Ni(110), and Ni(111). Then, we investigated the structural properties on the surface layers with increasing temperature up to the melting points. The simulation results exhibit that with the temperature increasing, the (110) surface firstly disorders, followed by the (100) surface, while the stability of the (111) surface is maintained until near the melting point. The disorder of surface layer atoms diffuses from the surface to the inside of the crystal lattice. With the density of atoms decreasing on the surface, the premelting effect also increases, being most pronounced on Ni(110) which corresponds to the lowest surface density. This conclusion is linked with the behavior found for the BCC transition metal Fe in our previous simulation study. [ABSTRACT FROM AUTHOR]

• The crystal morphology of the CL-20/TFAZ cocrystal was predicted using modified attachment energy in solvent. • Crystal shape becomes closer to a stereoscopic shape in IPA/EA solvents. • The interaction between CL-20/TFAZ cocrystal and various solvents was analyzed using radial distribution function. • Mean square displacement method was used to analyze the diffusion coefficients of various solvents in CL-20/TFAZ cocrystal. Crystal morphology of CL-20/TFAZ cocrystal in vacuum was predicted using the attachment energy (AE) model. Additionally, the modified attachment energy (MAE) model and molecular dynamics (MD) method were utilized to predict the crystal morphology of CL-20/TFAZ cocrystal in four different binary solvents, namely, isopropyl alcohol (IPA)/acetone (AC), IPA/dimethyl sulfoxide (DMSO), IPA/ethyl acetate (EA), and IPA/water (H 2 O). The radial distribution function (RDF) between the solvent and crystal surface and the mean square displacement (MSD) of the solvent were calculated. The findings showed that the morphology of CL-20/TFAZ cocrystal in vacuum was an irregular polyhedron with eleven important growth surfaces: (0 0 1), (1 −1 0), (1 1 0), (1 0 0), (0 1 1), (0 −1 1), (1 0 −1), (0 2 0), (0 −2 0), (1 1 −1), and (1 −1 −1), with the (0 0 1) surface having the highest area ratio of 31.693 %. The crystalline morphology in IPA/AC, IPA/DMSO, and IPA/EA solvents was block-shaped, while it was rod-shaped in IPA/H 2 O. Comparing the RDF values of the four solvents, IPA/H 2 O exhibited the largest g(r) value and could more easily adsorb onto the crystal surface of CL-20/TFAZ cocrystal. Interestingly, IPA/H 2 O solvent had the smallest MSD value, suggesting the slowest diffusion rate, while IPA/AC solvent exhibited the fastest diffusion rate. Overall, IPA/EA solvents were more suitable for the formation of CL-20/TFAZ cocrystal. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) crystal is a third-generation semiconductor material, which is widely used in the fields of radio frequency components, aerospace, new energy vehicles, etc. The anisotropy of 4H–SiC leads to differences in material removal characteristics of different crystal surfaces, which influences the design of process parameters for SiC crystal polishing. A model of single abrasive scratching 4H–SiC crystal was established using molecular dynamics. The effect of scratching speed and depth on the material removal characteristics and the wafer surface morphology was investigated when a single abrasive scratches the C surface and Si surface. Scratching experiments were conducted to verify the model by measuring scratch cross-sectional area, scratch profile, and surface roughness. The simulation results reveal that compared to the Si surface, the distribution range of high hydrostatic stress of the C surface is less, resulting in fewer amorphous atoms and easier dislocation, which means the C surface is more favorable for getting plastic removal and obtaining better surface quality. The experiment data suggested that the C surface has a smaller surface roughness and a friction coefficient, and the cross-sectional area of the scratch is larger than that of the Si surface. Under low-speed conditions, the influence of anisotropy is more pronounced. Consistent with the simulation result, the material removal characteristics of the C surface are better than those of the Si surface when single abrasive scratching 4H–SiC crystal. [ABSTRACT FROM AUTHOR]

Currently, laser-induced damage is a prominent focus in the field of ultrafast laser micro/nano processing. This article focused on the potential formation thickness of the ultrafast laser-induced sapphire crystal surface recast layer. To investigate the influence of laser parameters and crystal orientation on the recast layer potential formation thickness at the atomic scale, a molecular dynamics model of laser irradiation sapphire crystal was constructed. Experiments of laser-induced recast layer formation were carried out, and the effects of laser fluence, pulse width, and wavelength on the surface recast layer were analyzed. The results show that the ejected atom start formation time is significantly influenced by pulse width, while the potential formation thickness of the recast layer is mainly influenced by the deposited laser energy. Moreover, under the same laser energy, the damage extent in sapphire crystal caused by laser irradiation along the (0001) orientation is significantly weaker compared to irradiation along the (1–100) and (11–20) orientations. This article could provide theoretical and process references for suppressing the ultrafast laser-induced sapphire crystal surface recast layer formation. [ABSTRACT FROM AUTHOR]

aligning surface for preorientation of low molecular weight liquid crystals in a bulk. The brush is built by grafting the polymer chains of a side-chain molecular architecture, with the side chains terminated by a chromophore unit mimicking the azobenzene unit, to a substrate. When irradiated with ultraviolet light, the chromophores photoisomerize into a non-mesogenic cis state and the whole system turns into an ordinary polymer brush with no orientationalorderandtwostates:thecollapsedandstraightenedone,dependingonthegraftingdensity.When irradiated with visible light, the chromophores photoisomerize into a mesogenic trans state, resulting in formationofatransientnetworkbetweenchainsbecauseofastrongattractionbetweenchromophores. Spontaneous self-assembly of the brush in these conditions results in an orientationally isotropic polydomain structure. The desired uniaxial planar ordering of chromophores within a brush can be achieved at certain temperature and grafting density intervals, as the result of a two-stage preparation protocol. An external stimulus orients chromophoresuniaxiallyatthefirststage. Thesystemisequilibratedatthesecondstageatagiventemperatureand with the external stimulus switched off. The preoriented chromophores either keep or loose their orientations depending on the strength of the memory effect inherent to a transient network of chains that are formed during the first stage, similarly to the case of the liquid crystalline elastomers, where such effects are caused by the covalent crosslinks. [ABSTRACT FROM AUTHOR]

Dendrite formation occurs on Li, Na, and Mg metal anodes in rechargeable batteries, and is a safety challenge, as well as a limiting factor for increasing energy- and power density. However, the behaviour of the dendrites differs depending on the anode material. In this study, we investigate the local bulk and surface crystal structure of Li, Na, and Mg surfaces to shed light on how differences in the morphology and structure of the anode surface and its metal deposits can explain differences in dendrite formation on Li, Na, and Mg anodes. The local bulk- and surface structure are found using molecular dynamics simulations in combination with the surface adaptive common neighbour analysis, and indicate that Li and Na surfaces are more prone to surface instabilities and formation of protrusions than Mg surfaces, which remain flat and hexagonal close-packed even near room temperature. Additionally, the equilibrium shapes of the Mg deposits obtained from density functional theory assume more flat and hexagonal shapes than the Li and Na deposits. Together, these results shed light on atomic mechanisms that may contribute to the different propensities of Li, Na, and Mg metal anodes to form dendrites. [ABSTRACT FROM AUTHOR]

In ultra-precision machining, material anisotropy has an essential impact on surface generation and subsurface damage. In this work, the molecular dynamics method is applied to create the diamond nano-cutting models of Ni-based single crystal (NBSX) superalloy workpieces with different crystal orientations, and the surface/subsurface damage characteristics, crystal structure changes, cutting force, and atomic temperature and stress are discussed. The results show significant differences in surface/subsurface quality, crystal structure transformation, cutting force, atomic temperature and stress distributions and dislocation density obtained from nano-cutting workpieces along different crystal orientations. In four groups of workpieces, the surface/subsurface quality is used as an evaluation index, which shows that the [110](001) crystal orientation has the best cutting effect, and the [111](1 ‾ 10) crystal orientation is the worst cutting direction. This work reveals the damage generation mechanism of the machined surface/subsurface of NBSX superalloy on an atomic scale, which provides technical support for improving machining quality and optimizing machining parameters. [Display omitted] • Surface/subsurface damage characteristics are formed by different crystal orientations. • The workpiece with the [110](001) crystal orientation has the optimal surface/subsurface quality. • Material stress induces the formation of dislocations and defects, and three deformation zones appear in the tool-to-workpiece contact area. • The temperature drop point is closely related to chips and side flow. [ABSTRACT FROM AUTHOR]

Arginine‐modified polyepoxysuccinic acid (Arg‐PESA) was used as a scale inhibitor to study its anti‐scaling and anti‐corrosion performance. The existence of arginine groups enhances the adsorption and chelation of calcium substances, thus inhibiting the formation of a calcium scale. The effects of temperature, scale inhibitor concentration, pH, and calcium ion concentration on scale inhibition performance were studied. The morphologies and structures of the calcium scale and carbon steel coupons were observed and characterized by spectroscopic and microscopic methods. The interaction between Arg‐PESA and different crystal surfaces of calcium carbonate was simulated by molecular dynamics to elucidate the anti‐scaling mechanism. The addition of Arg‐PESA also significantly enhanced the dispersion of iron oxide. [ABSTRACT FROM AUTHOR]

Solvents can dramatically affect molecular crystals. Obtaining favorable properties for these crystals requires rational design based on molecular level understanding of the solid–solution interface. Here we show how atomic force microscopy combined with molecular dynamics simulations can be utilized for understanding critical surface properties, namely crystallinity and hydrophobicity, as crystals are exposed to water–ethanol mixtures. We report the formation of dynamic heterogeneous disordered surface (DHDS) layers at the solid–solution interface. The observed DHDS layer was affected by the solvent composition and a variation in the water–ethanol ratio caused significant changes in surface properties. [ABSTRACT FROM AUTHOR]

The release of clusters from the surface of PuO 2 nanocrystals caused by the alpha decay collision cascades was simulated using the molecular dynamics. The clusters containing up to several hundred particles were recorded. The obtained size distributions of the clusters were characterized by relatively high probabilities of the formation of large clusters. The total kinetic energy of the released material reached tens of percent of the total energy of the collision cascade. Single ions, both plutonium and oxygen, could have kinetic energies of up to several thousand electron-volts. The electric charge of the clusters in most cases was close to zero, although clusters with significant negative charges were also observed. [ABSTRACT FROM AUTHOR]

The advanced spiral growth model that considers the thermodynamics and kinetics aspects of the adsorption process is applied to predict the growth habits of the nitroguanidine crystal in water and γ-butyrolactone. The molecular dynamics simulations were performed to search for the equilibrium state of the interface model. The predicted results show that the crystal shapes of nitroguanidine in water and γ-butyrolactone are needlelike and flake-like shape, respectively, which agrees remarkably well with the experiment. In water, the (011) face constitutes an overwhelming 96.17% of the total crystal surface area, and the crystal grows rapidly along the [111] direction. In γ-butyrolactone, the (011) face is exposed, but its area only accounts for 15.56%. The (011) face and the mostly exposed (001) face form a surrounding surface in a flake-like shape. Furthermore, periodic bond chains are used to analyze the growth process of different crystal faces. [ABSTRACT FROM AUTHOR]

Solution crystallization is a common technique to grow advanced, functional crystalline materials. Supersaturation, temperature, and solvent composition are known to influence the growth rates and thereby properties of crystalline materials; however, a satisfactory explanation of how these factors affect the activation barrier for growth rates has not been developed. We report here that these effects can be attributed to a previously unrecognized consequence of solvent fluctuations in the solvation shell of solute molecules attaching to the crystal surface. With increasing supersaturation, the average hydration number of the glutamic acid molecule decreases and can reach an asymptotic limit corresponding to the number of adsorption sites on the molecule. The hydration number of the glutamic acid molecule also fluctuates due to the rapid exchange of solvent in the solvation shell and local variation in the supersaturation. These rapid fluctuations allow quasi-equilibrium between fully solvated and partially desolvated states of molecules, which can be used to construct a double-well potential and thereby to identify the transition state and the required activation barrier. The partially desolvated molecules are not stable and can attach spontaneously to the crystal surface. The activation barrier versus hydration number follows the Evans-Polanyi relation. The predicted absolute growth rates of the a-glutamic acid crystal at lower supersaturations are in reasonable agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

We introduce Interfacial Line Defect Analysis (ILDA), a method for identifying and extracting interfacial dislocations and disconnections with little-to-no input from the user on the nature of the interface. By simply providing the orientations and coherency strains for the crystals in a coherent reference state of the interface, ILDA provides exact Burgers vectors. Alternatively, these orientations and strains can be estimated using local atomic deformation gradients, making ILDA fully automated and providing estimated Burgers vectors. ILDA also determines the step height associated with each defect line segment, in case the associated defect is a disconnection. The heart of the method is the identification of atoms residing at co-incidence sites between the two crystals and the construction of a surface mesh connecting these sites that is used to compose Burgers circuits and insert defect line segments. We demonstrate the performance of ILDA in two test cases: a twist grain boundary and a phase boundary. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • With the decrease of temperature, the order degree of the system is strengthened and the fluidity is weakened. • The diffusion coefficient of the H 2 O molecule is greater than that of the n C 5 H 12 molecule by a factor of ∼2. • At the same temperature, the diffusion coefficient of the n C 24 H 50 molecule in n C 5 H 12 is greater than that in H 2 O. • At temperatures of 50–20 °C, n C 24 H 50 molecules precipitate from the oil and gather on the pipe wall surface. Wax deposition on the inner wall of oil pipes, sucker rods, oil- and gas-gathering pipelines and equipment caused by wax crystals has been a challenging problem in the petroleum industry. At present, most of the marine terrestrial transitional facies and continental shale oil and gas being explored and developed in China have high-wax-content volatile oil or condensate, and many shale oil and gas wells have been seriously blocked by wax deposition. In this work, the wax deposition behavior of the binary alkane mixture n C 5 H 12 – n C 24 H 50 at different temperatures under the condition of water wetting of a pipe wall was studied through molecular dynamics simulation. When the temperature is 130–70 °C, the wax molecules are loosely distributed without obvious aggregation, and the pipe wall is mainly occupied by water molecules, exhibiting a water-wetting state. With the decrease in temperature, the distance between n C 24 H 50 molecules decreases correspondingly, which enhances the interaction between wax molecules and increases the probability of mutual aggregation. When the temperature is 50 °C, a small amount of n C 24 H 50 molecules pass through the water molecular layer and gather on the pipe wall. When the temperature is <50 °C, the binding energy between the crystal surface of the pipe wall and the molecule n C 24 H 50 exhibits a first-order phase transition, and the molecule n C 24 H 50 can more easily bind to the pipe wall than the molecule H 2 O. When the temperature is 40–20 °C, the aggregation amount of n C 24 H 50 molecules on the pipe wall further increases, exhibiting an obvious crystallization tendency, and a small amount of n C 5 H 12 molecules begin to aggregate with n C 24 H 50 molecules through the water molecular layer on the pipe wall. At the same temperature, the diffusion speed of n C 24 H 50 molecules in n C 5 H 12 is faster than that in H 2 O. [ABSTRACT FROM AUTHOR]

TOC Graphic Interfacial water and protein orientation modify the load-deformation response, conformations and the non-bonded interactions between protein with the mineral surface. Enamel is a composite bioceramic that covers teeth. Here, based on molecular dynamic (MD) simulation, we seek a better understanding of the interactions between the enamel matrix proteins with hydroxyapatite (HAP) crystal surfaces. These interactions occur during enamel formation and are responsible for controlling the formation of high aspect ratio carbonated hydroxyapatite nanocrystallites, whereas, in mature enamel, they are implicated to alter the mechanical properties of mature enamel to yield a tough composite that resists fracture during chewing. We choose an archetypal matrix protein known as tyrosine-rich amelogenin peptide (TRAP), which is retained among the HAP crystallites of mature enamel. Our findings provide molecular details to the emerging blueprint needed to engineer a biologically inspired enamel restorative material. [ABSTRACT FROM AUTHOR]

• For the first time mass transfer by 2-crowdion is studied for realistic 3D crystal. • Impacts by Pt atom and Pt2 molecule on (1 0 1) surface of Pt crystal are compared. • Many-body EAM potential is used in molecular dynamics simulations. • Properly oriented molecule needs much smaller energy to initiate mass transfer. • Molecule impact can initiate propagation of supersonic 2-crowdion in platinum. Crystal surface bombardment by atoms or molecules, neutral or ionized, occurs both in ambient conditions and in many technological operations, such as surface plasma treatment, ion implantation, etc. Recently, it was established that the impact of a molecule initiates the mass transfer in the one-dimensional Frenkel-Kontorova atomic chain more efficiently than that of a single atom. This is explained by the fact that the atom can initiate only a very sharp, fast-moving crowdion (anti-kink), which requires relatively high energy, while the molecule is able to initiate a less localized crowdion with considerably lower velocity and energy. In the current study, by means of molecular dynamics simulation, for the first time, this phenomenon is studied for a realistic 3D model of platinum crystal. We compare the efficiency of single Pt atom impact and Pt 2 molecule impact on the (1 0 1) surface of fcc Pt crystal for the initiation of mass transfer in the material by crowdions. It is revealed that in order to generate a crowdion moving inside the crystal, the properly oriented molecule needs an order of magnitude smaller energy than single atom. This considerable reduction of required energy happens when the molecule is oriented perpendicularly to the crystal surface and hits the crystal along a close-packed atomic row. Furthermore, it is revealed for the first time that the molecule with sufficiently large velocity can initiate the so-called supersonic 2-crowdion, which travels longer distances in the crystal than the classical supersonic crowdion having same or even higher energy. Our results can be useful for understanding and prediction the mass transfer during technological applications where bombardment by atomic clusters is employed to modify and improve mechanical or functional properties of surfaces. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The role of interfacial fluctuations can be quantified using cumulant expansions. • Fluctuations near solid-liquid interface depend on the type of crystal surface. • The dampening of fluctuations depend on the type of crystal surface. • The actual contribution of interfacial fluctuations is small, but non-negligible. Abstract Transverse correlations (TCs) denote the correlations between density-fluctuations along the plane parallel to a solid-liquid interface. We use molecular simulations to investigate the TCs in a model fluid near static 100, 110 and 111 faces of BCC, FCC, and SC crystals of model solids. We use the cumulant expansions of solid-liquid interfacial free energies to quantify the contribution of TCs to the interfacial free energy. We approximately decompose the above contributions into those from TCs of different ranges. Our results show that the solid-fluid attractive interaction strongly dampens the TCs, and the extent of dampening depends on the exposed face of the crystal. We also observe that the contribution from TCs near the selected surfaces differ significantly even in absence of solid-fluid attractive interaction. Overall, our results indicate a great potential for tuning the solid-liquid interfacial fluctuations by altering the crystalline nature of solid surface. [ABSTRACT FROM AUTHOR]

Highlights • Pt3Al intermetallic alloy supports near-surface discrete breathers (DB). • Properies of DB depend on surface orientation and termination. • DB can localize energy about 1 eV. • DB can help to overcome potential barriers for structure transformations. Abstract It is known that defect-free crystals can support spatially localized, large amplitude vibrational modes with frequencies outside the linear phonon spectrum. Such excitations are called discrete breathers (DB) or intrinsic localized modes. So far, for 3D crystals DB were considered only in the bulk. In the present molecular dynamics study, for the first time, we demonstrate that DB can be excited at the low Miller indices surfaces of the Pt 3 Al intermetallic alloy. It is shown that properties of the DB depend essentially on the surface orientation and termination, as well as on DB polarization. The study of DB at crystal surfaces is important because they can localize energy of order of 1 eV, which can reduce the potential barrier for local structure transformation or a chemical reaction. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

The adsorption of water and ions on ettringite crystal, an important hydration product in the cement material, is fundamental to the durability of cement-based material. In this study, molecular dynamics was utilized to investigate the molecular structure, dynamics and interfacial bonding for the water and ions in the vicinity of ettringite crystal surface. The aluminate octahedron and sulfate ions in the surface of ettringite provide plenty of oxygen sites to accept H-bond from the water molecules in the interfacial region. The highly solvated surface calcium ions can strongly attract the neighboring water as their coordinate atoms. The hydrophilic nature of the ettringite interface results in the dramatically different feature of the water molecules on the ettringite surface, such as high dipole moment, ordered organization, good orientation preference and slow diffusivity. Furthermore, with gradually increasing simulation time, the calcium ions, aluminate and sulfate species in the crystal surface diffuse into the solution, resulting in the dissolution of the ettringite crystal and disturbance of the ordered interfacial topology. The six-coordinated aluminum hydroxyl groups transform to the aluminate tetrahedron, as they dissolve in the solution. Additionally, the chloride and sodium ions have different adsorption mechanism on the crystal surface. While the sodium ions are associated with the oxygen atoms in aluminate octahedron and sulfate ions by Na O ionic bond and immigrate into the inner region of the dissolved crystal, the chloride ions can form the ionic pairs with the calcium ions, accumulating to cluster in the outer layer region. As compared with the chloride adsorption, the ettringite crystal has better immobilization ability on the cation ions due to the stable Na O connection with long resident time. [ABSTRACT FROM AUTHOR]

We studied analytically and numerically the growth rate of a crystal surface growing by several screw dislocations. We observed some discrepancy between the growth rates computed by our level set method (J. Sci. Comput. 2015, 62, 831-874) and those reported by the classical paper of Burton et al. (Philos. Trans. R. Soc. London A 1951, 243, 299-358). To resolve the discrepancy, we propose a few improved estimates on the growth rate in several configurations. In particular, we give a quantitative definition of the critical distance of corotating screw dislocations under which the effective growth resembles that of a single spiral. We further study the growth rate of a crystal surface containing a group of screw dislocations. The proposed new estimates are in agreement with numerical simulations using the algorithm published by the authors (J. Sci. Comput. 2015, 62, 831-874). [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were carried out to study the polymer-bonded explosives (PBXs) where the explosive base was the well-known high energy co-crystal compound, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT), and the polymer binders were fluorine rubber (F, fluorine resin (F, polyvinyl acetate (PVAc) and polystyrene (PS), respectively. The binding energies, pair correlation functions (PCFs) and mechanical properties of the PBXs were reported. According to our theoretical results of binding energies, the compatibility of the PBXs is predicted to be in the following order: CL-20/TNT/PVAc CL-20/TNT/F CL-20/TNT/PS CL-20/TNT/F. The binding energies of the PBXs on three crystalline surfaces, (100), (001), (010), of the CL-20/TNT co-crystal were also compared: CL-20/TNT(100)CL-20/TNT(001)CL-20/TNT(010) for F, F, and PS; CL-20/TNT(001)CL-20/TNT(100)CL-20/TNT(010) for PVAc. The PCF analysis reveals that there exist H-bonds between H and O, F, and N atoms on all three interfaces and among all H-bonds, N H-bond has the fewest number. For the CL-20/TNT co-crystal, the moduli can be reduced by adding a small amount of the polymer binders but the ductility can be prolonged only by F and F. [ABSTRACT FROM AUTHOR]

Metals corrosion and scales deposition are two serious problems of heavy burden in most industries. Both problems can be mitigated by adding special chemicals capable of being adsorbed on metallic surfaces as well as on scale growing crystal surfaces. Efficient materials should be rich in functional groups containing heteroatoms and/or π bonds for supporting their adsorbability on surfaces. In the present work, four novel pyrazole derivatives were synthesized and characterized for their structures using elemental analysis and spectroscopic tools. The tested compounds were fabricated by treating 2,3-diaryloxirane-2,3-dicarbonitriles with different nitrogen nucleophiles. The density functional theory (DFT) was then applied to explore the structural and electronic characteristics of these materials. Molecular dynamics simulation was also run to scrutinize the ability of the prepared compounds to act as corrosion inhibitors and antiscalant agents by adsorbing on Fe and CaSO 4 surfaces. [ABSTRACT FROM AUTHOR]

An approach to constructing a biased potential for hyperdynamic simulation of atomic systems is considered. Using this approach, the diffusion of an atom adsorbed on the surface of a two-dimensional crystal and a vacancy in the bulk of the crystal are simulated. The influence of the variation in the potential barriers due to thermal vibrations of atoms on the results of calculations is discussed. It is shown that the bias of the potential in the hyperdynamic simulation makes it possible to obtain statistical samples of transitions of atomic systems between states, similar to those given by classical molecular dynamics. However, hyperdynamics significantly accelerates computations in comparison with molecular dynamics in the case of temperature-activated transitions and the associated processes in atomic systems. [ABSTRACT FROM AUTHOR]

• Polyethylene glycol was first used to regulate the carnallite decomposition. • KCl grade was enhanced by 10.33% through polyethylene glycol. • Regulation mechanism was explained by AFM characterization and MD simulation. Currently, the "crystallization-flotation" process is widely used for the industrial production of KCl. However, the significant aggregation of KCl and NaCl in the decomposition-crystallization stage of carnallite leads to inefficient separation of the two particles in the flotation stage, which restricts the production of high-grade KCl. In this study, environmentally friendly polyethylene glycol (PEG) was used to regulate the decomposition-crystallization of carnallite for the first time, and the high-grade KCl was successfully prepared by reducing the degree of crystal aggregation. The crystals were characterized by SEM-EDS, FT-IR, XRD and AFM, and it was found that PEG which average Mn 800 (PEG 800) could adsorb on the crystal surface and effectively disperse NaCl and KCl. It was also found that there are two mechanisms by which PEG 800 achieves dispersion. On the one hand, PEG 800 micelles contain polyoxyethylene chains with large steric repulsion, which can prevent the adhesion of particles. On the other hand, PEG 800 can weaken the electric potential on the surface of KCl and NaCl and reduce the electrostatic interaction force between the particles. Finally, the behavior of Na, K, and Cl before and after the addition was simulated by molecular dynamics, and molecular dynamics calculations showed that PEG 800 could weaken the effect of NaCl on KCl. [ABSTRACT FROM AUTHOR]

Crystal-melt interfacial free energies are important ingredients in predicting the nucleation barrier for polymers to crystallize. Experimental measurement of polymer crystal-melt interfacial tensions is challenging, particularly for crystal facets other than the lamellar surfaces. We propose a simple way to obtain the interfacial free energy for any polymer crystal surface and melt using molecular dynamics simulation. We measure the force on a simulated nanoscale "plunger", that restrains a melt from flowing into the gap between two crystals cleaved along the (100) plane. This gives the difference between the crystal-vacuum and crystal-melt interfacial free energies. Separately, the crystal-vacuum interfacial free energy is obtained by measuring the force required to hold two crystals apart and integrating the force with respect to distance. We obtain the crystal-melt interfacial free energy by subtracting the above values. Results from this method applied to n-alkanes can be compared to measurements of the homogeneous nucleation barrier. [ABSTRACT FROM AUTHOR]

The solvent has a significant effect on the crystal morphology of 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP). The attachment energy model was employed to predict the crystal morphology of MTNP in vacuum, and the main habit facets were obtained. On this basis, the interface models between the ethanol solvent and the crystal surface were constructed and simulated by molecular dynamics method, their interactions were analyzed in detail by radial distribution function and mean square displacement. The final crystal morphology of MTNP in ethanol solvent was obtained using the modified attachment energy model. The results show that MTNP crystals simulated in vacuum have up to 10 habit faces, of which the (1 1 0) and (2 0 0) faces are morphologically more important, accounting for 43.67% and 10.59% of the total surface area, respectively. There is significant hydrogen bonding interaction between the crystal surfaces and the ethanol solvent, which alters the relative growth rates of the different faces and leads to changes in the crystal morphology. The diffusing ability of the ethanol solvent on the crystal face also has a non-negligible effect on the interaction, and the stronger the diffusing ability, the more favorable the interaction. In the presence of ethanol solvent, the (2 0 0) surface disappears and the crystal morphology of MTNP shows a fusiform. • Investigating the crystal morphology of MTNP in vacuum. • Constructing interfacial models of MTNP crystal faces and ethanol solvent. • Studying the interactions between solvent and crystal faces. • Predicting the crystal morphology of MTNP in ethanol solvent. [ABSTRACT FROM AUTHOR]

Snapshots of evolution of deuterium bubbles below the (1 1 1) surface of tungsten, exposed to the flux of 6. 24×1028 m−2s−1 and 80 eV deuterium atoms at 300 K. The red spheres represent the tungsten atoms and the blue spheres represent the deuterium atoms. The black dashed lines represent the original boundary of the tungsten atoms. [Display omitted] • D bubble evolution process is divided into three stages: formation, growth, and burst and it are significantly influenced by temperature, flux, and energy, which is revealed by molecular dynamics methods. • The evolution of deuterium bubbles under various crystal surfaces reveals that it was found to be more difficult under a surface with a higher crystal face density. • By calculating the internal pressure, volume, and molecular ratio (D in D 2)/D of deuterium bubbles, the mechanism of deuterium atoms forming molecules and then forming deuterium bubbles is proposed. Using molecular dynamics simulations, the Tersoff-potential was used to investigate the evolution of deuterium (D) bubbles in tungsten (W). This work documents the entire evolution process of D bubbles: formation, growth and burst. The effects of flux, temperature and incident energy of D on the evolution and position of D bubbles were discussed. Temperature and flux together affect the time required for D bubble formation, and energy has a significant effect on depth. At 300 K, single-crystal tungsten surfaces (0 0 1), (1 1 0), (1 1 1), and (1 1 2) were bombarded by D atoms with 80 eV energy and 6.24 × 1028 m−2s−1 flux. Although all D bubbles go through three stages, the pressure, volume, and the ratio of (D in D 2)/D inside bubbles can tell the difference between the four surfaces. Under the same simulation conditions, the evolution of D bubbles under a surface with a higher crystal face density was found to be harder. [ABSTRACT FROM AUTHOR]

AlSiC composites is a common material to make IGBT substrate due to its adjustable coefficient of thermal expansion which can be well matched with the chip and ceramic substrate to prevent the fatigue failure. Understanding the role of SiC surface morphology or crystal orientation might have an important influence on the proper control of the solid-liquid interface transmission in the process of preparing SiC reinforced aluminum matrix composites. To quantify the solid-liquid interaction, the molecular dynamics study is performed on the wetting characteristics of molten aluminum droplets on the 4H–SiC surface. Two SiC surface structures including rectangular-groove and wedge-groove are firstly adopted to analyze the effect of surface morphology on the wettability. Then, the wetting characteristics of Al droplets on two SiC crystal orientations including (110) plane and (111) plane are studied. The corresponding contact angles θ in the four Al/SiC systems are 124.81°, 126.65°, 105.72° and 97.35° respectively. It is found that the atomic surface morphology and crystal orientation playing important roles in the wettability of 4H–SiC. High hydrophobic is observed on the rectangular-groove and wedge-groove surface, while the wettability of the (110) plane and (111) plane is between wetting and hydrophobicity. [ABSTRACT FROM AUTHOR]

Nickel-based single crystal alloys are widely used in aerospace, national defense and other fields because of their excellent properties (excellent strength, high temperature creep resistance and corrosion resistance). At present, its machining accuracy is very high, and high machining surface quality is required. In the sub nano and near atomic scale (SN-NAS) cutting process, the crystal orientation of workpiece has an important impact on the internal dislocation nucleation and expansion and surface material removal. These changes will affect the evolution process of subsurface defects and have an important impact on the surface quality. The SN-NAS cutting models are established, and the relationship between dislocation emission and energy change is deduced. The cutting models of nickel-based single crystal alloys with different crystal orientations were established by the molecular dynamics method. It is found that dislocations are emitted along the direction perpendicular to the cutting surface. Due to the different crystal orientation of the workpiece, the dislocation slip direction presents anisotropy. The plastic deformation of the workpiece is closely related to dislocation slip and stacking fault propagation. Due to the difference in lattice arrangement, dislocation slip orientation and surface energy, the surface roughness shows strong anisotropy. The work hardening behavior is determined by the change of micro defect structure and dislocation density in the workpiece. At the same time, it is closely related to the movement of material slip system and the self-hardening and latent-hardening of dislocations. This study analyzes the formation mechanism of the subsurface deformation layer and how the change of crystal orientation affects the evolution of the subsurface deformation layer, so as to provide technical support for the development of SN-NAS cutting of nickel-based alloy. The figure shows the model of dislocation emission (a1) and relationship of angle-energy difference(a2) The surface roughness of nickel-based single crystal alloy after cutting (b)Shockley dislocation density(c) self-hardening and latent-hardening between slip systems(d). [Display omitted] 1 From the perspective of theoretical analysis, the relationship between dislocation emission angle and energy difference under different dislocation slip lengths is established. 2 The reasons for the anisotropy of dislocation emission angle and dislocation slip direction are analyzed by the molecular dynamics method. 3 The reasons for the anisotropy of surface roughness are analyzed from the perspectives of surface energy, atomic arrangement, atomic dense arrangement et al. 4 The anisotropy of work hardening is studied from the aspects of dislocation density, micro-defect evolution, dislocation self-hardening and latent-hardening between slip systems. [ABSTRACT FROM AUTHOR]

AlSiC composites is an irreplaceable material for high temperature semiconductor devices due to its unique performance of high thermal conductivity, low thermal expansion coefficient and bending strength. Understanding of the atomic level interactions between SiC and Al is paramount important. This leads to appropriate control on the transport process at the solid-liquid interface in the preparation of SiC reinforced aluminum matrix composites. To characterize the solid-liquid interaction, the aim is to perform molecular dynamics study on the wetting behavior of molten aluminum droplets on the 3C–SiC surface. The wettability of four crystal surface structure including Si-terminated, C-terminated, rectangular groove, wedge groove was characterized. The corresponding contact angles θ were 113.52°, 80.11°, 108.93° and 132.83° respectively. It was found that the atomic surface terminals and crystal surface morphology play an important role in the wetting behavior of 3C–SiC. High hydrophilic was observed on the C-terminated surface, while the wedge-shaped surface showed high hydrophobic. These theoretical findings demonstrate the effective modeling strategies when using wetting behavior as an interface modeling framework. [ABSTRACT FROM AUTHOR]

• Ice growth speed is determined by atomic mobility and thermodynamic driving force. • A lower surface energy of ice crystal leads to a slower ice propagation. • Surface interaction rearranges ice crystal or graphene flakes during freezing. • Due to the rearrangement, ice grows faster in parallel to the graphene surface. The influence of thermodynamic and structural conditions on water-ice phase change process was investigated with consideration of graphene-water surface interactions for fundamental understanding and effective control of freezing propagation. The phase change propagation as well as structural and energetic properties during the phase change were examined by analyzing atomic data from molecular dynamics simulations. The freezing propagation speed is affected by the competition between atomic mobility and thermodynamic driving force for phase change, which causes an optimal temperature for fast ice growth to appear at 252 K. In addition, the water-ice interfacial energy, which depends on the orientation of the water-contacting ice surface, changes interfacial structural stability and thus freezing propagation, i.e., a higher interfacial energy leads to a faster ice propagation. Therefore, we suggest that the water-ice phase change propagation can be controlled by adjusting the orientation of ice crystal. The surface interactions, or graphene-water interactions in this research, affect the energetics near the water-surface interface. The energetic change rearranges the ice crystal or surface structures to reach the most stable ice-surface configuration or minimum energy state, in which the basal plane of the ice crystal is parallel with the graphene surface. As ice propagation is the slowest perpendicular to the basal plane, ice can grow faster parallel to graphene surface. The findings from this study provides insights to ice propagation control mechanisms for versatile freeze casting and its broader applications. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were used to investigate aggregation of surfactants at the solid–liquid interface at different surfactant concentrations. For these studies simulations of the sodium dodecyl sulfate (SDS) surfactant with a graphite surface were carried out. At low concentrations the SDS molecules aggregated in slices of cylinders attached to the solid surface, whereas at slightly higher concentrations the structures showed irregular shapes. When the concentration was again increased to a higher value, the molecules aggregated in a more complex structure, an irregular aggregate on the top of a semicylinder adsorbed on the graphite surface. From the present results more insights about the internal structure of the aggregates were observed than in actual experiments, e.g., it was found that the SDS tails arrayed in well-defined layers close to the graphite surface. More over, from the internal structure it was possible to show a structural transition driven by an increment in the surfactant concentration which, to the best of our knowledge, has not been studied from a molecular point of view. Therefore the transition was studied in terms of the height of the structures. Along with these studies adsorption of the aggregates, by calculating contact angles, and adsorption isotherms were also analyzed. Finally, investigations of the surface coverage with the concentration showed that this quantity did not change considerably with the concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D model is proposed to explain the material removal mechanism in nano-machining of FCC crystal. • The MD simulation methods and the nano-scratching experiments were conducted to verify the theoretical model. • Both the chip thickness and ploughing width can be accurately calculated by the model. • The results indicate that the crystal orientation determines the transformation between chip removal and ploughing. • The 3D model is only valid for the nano-machining, where tool width and uncut chip thickness are both at the nanoscale. In machining operations, investigating the transformation between chip removal and ploughing is crucial to understand the material removal mechanism, which is also the basis for analyzing the machining process, such as calculating cutting force and predicting minimum uncut chip thickness (MUCT). In this study, an analytical model was proposed to predict the chip thickness and ploughing width for FCC crystal materials under arbitrary crystal orientations in nano-machining. The molecular dynamics (MD) simulation methods and the nano-scratching experiments were conducted to verify the theoretical model under two representative crystal orientations. The results indicate that the crystal orientation determines the transformation between chip removal and ploughing. Moreover, according to surface crystal orientation, machining direction, tool radius, and uncut chip thickness, the chip thickness and ploughing width can be calculated in nano-machining. The model can be applied to the nano-machining process of FCC crystals that achieve the plastic deformation by the (110){111} slip system, where tool size and uncut chip thickness are at the nanoscale. [ABSTRACT FROM AUTHOR]

[Display omitted] • The theoretical calculation explored the interactions of PBTCA and calcium carbonate firstly. • PBTCA performed excellently in inhibiting the deposition of calcium carbonate. • PBTCA could induce the lattice distortion of CaCO 3 from calcite to vaterite at optimum concentrations. • PBTCA with outstanding structure was beneficial to enhance the adsorption of Ca2+. The performance and mechanism of typical scaling inhibitors, i.e., 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), in inhibiting calcium carbonate scaling were investigated. Results of the static experiment at 30 °C and 80 °C revealed that at the optimal concentration, the scaling inhibition efficiency of PBTCA was superior to that of HEDP. Additionally, X-ray powder diffraction evaluation demonstrated that in comparison with HEDP, PBTCA inhibited the growth of the (1 0 4) crystal plane of calcite more evidently. Scanning electron microscopy analysis indicated that the addition of scaling inhibitors induced the crystal transformation of CaCO 3 from calcite to aragonite. Molecular dynamics simulation also confirmed that the interaction of PBTCA with the (1 0 4) crystal surface of calcite is more apparent than that of HEDP. This observation was a consequence of the PBTCA being more negatively charged, as determined via a quantum chemical calculation. The calculation further indicated that the spatial distance of PBTCA to the (1 0 4) face of calcite was less due to stronger chelating ability and better suitability of the structure. As a result, in the tested temperature range, PBTCA exhibited the more effective inhibitory effect against calcium carbonate scaling. [ABSTRACT FROM AUTHOR]

Magnesium (Mg2+) is one of the most common impurities in calcite and is known to have a non-linear impact on the solubility of magnesian calcites. Using molecular dynamics (MD), we observed that Mg2+ impacts overall surface energies, local free energy profiles, interfacial water density, structure and dynamics and, at higher concentrations, it also causes crystal surface deformation. Low Mg concentrations did not alter the overall crystal structure, but stabilised Ca2+ locally and tended to increase the etch pit nucleation energy. As a result, Ca-extraction energies over a wide range of 39 kJ/mol were observed. Calcite surfaces with an island were less stable compared to flat surfaces, and the incorporation of Mg2+ destabilised the island surface further, increasing the surface energy and the calcium extraction energies. In general, Ca2+ is less stable in islands of high Mg2+ concentrations. The local variation in free energies depends on the amount and distance to nearest Mg in addition to local disruption of interfacial water and the flexibility of surface carbonate ions to rotate. The result is a complex interplay of these characteristics that cause variability in local dissolution energies. Taken together, these results illustrate molecular scale processes behind the non-linear impact of Mg2+ concentration on the solubility of magnesium-bearing calcites. [ABSTRACT FROM AUTHOR]

Improving the surface quality of the ZnGeP 2 crystal is an important way to expand its application range. Given the high difficulty of processing the ZnGeP 2 crystal, the research proposed a method of increasing the processing temperature of the material to expand the range of the plastic region, then improving the surface quality, the feasibility of the method was verified by heating assisted nanoindentation experiment and molecular dynamics simulation. The use of diamond tools to scribe the surface revealed the microscopic morphology changes of the ZnGeP 2 crystal under high temperatures. Finally, with the assistance of heating, the surface of ZnGeP 2 crystal was processed comprehensively by ultra-precision diamond fly-cutting machine, the experimental results showed that as the processing temperature increased, the surface quality of the ZnGeP 2 crystal gradually improved, and the surface roughness Sa could reach to 9.426 nm. The effectiveness of improving the surface quality through heating assisted cutting was verified, which had guiding significance for the processing of other hard and brittle materials. • The theory of improving the surface quality of ZnGeP 2 by heating assisted processing was put forward. • The feasibility of the theory was verified by molecular dynamics simulation and heating assisted nano-indentation. • The influence of heating assistance on the surface quality of ZnGeP 2 was analyzed. • The surface roughness of ZnGeP 2 obtained by heating assistance was higher, up to 9.426 nm. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were used to predict the thermal conductivity of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) along directions normal to the (011), (110), and (010) crystal planes. These directions were selected based on the measured morphological importance of the corresponding crystal surfaces. A reverse non-equilibrium MD approach was used wherein a constant heat flux is imposed along a prescribed direction and the resulting steady-state temperature gradient determined. The coefficient of thermal conductivity λ is the quotient of heat flux and temperature gradient (i.e. Fourier’s law). Finite-size effects and sensitivity to imposed heat flux were investigated. The results reveal a modest dependence of the conductivity on crystal orientation, significant finite-size effects, and low sensitivity to imposed flux so long as the Fourier’s law analysis is limited to the spatial interval in the simulation cell for which the temperature gradient is constant. Infinite-length thermal conductivities were estimated by linear regression of λ−1(L) versus reciprocal cell length L−1 for each direction. The predicted values are systematically larger, but within a factor of two, than most published experimental determinations, the latter of which were obtained for pressed-powder or composite samples rather than oriented single crystals. [ABSTRACT FROM AUTHOR]

During nanofabrication, the processing of different crystal faces along the surface of a workpiece varies because of size effects. The burr height and subsurface damage during nanogrinding of different crystal orientations in monocrystalline nickel are simulated by molecular dynamics in this study. The burr height and depth of the subsurface deformation layer are calculated quantitatively by atomic displacement, common neighbor analysis and dislocation analysis techniques. Among the directions considered in this paper, the burr height is the smallest when grinding in the (110)[110] direction, and the depth of the subsurface deformation layer is small when grinding along the (111) plane. This study demonstrates the effect of different slip paths on burr height and provides a reference for the actual processing of face-centered cubic crystals. [ABSTRACT FROM AUTHOR]

Sodium carboxymethyl cellulose (SCMC) effectively inhibits the growth of calcium carbonate fouling. In this work, molecular dynamics simulation is used to reveal the antifouling mechanism between SCMC and calcite surface. The configuration, radial distribution function, interaction energy between SCMC and calcite surface, and ability of SCMC to replace water molecules are analyzed. The results indicate that SCMC molecules regularly appear in the vicinity of 2.3 Å near the calcite surface for the different concentrations, and a strong interaction exists between them. The probability of SCMC appearing at ≈2.3 Å from the crystal surface increases with the SCMC concentration, and more SCMC molecules are adsorbed on calcite surface. Moreover, the interaction between SCMC and calcite surface increases with the increase of SCMC concentrations, and the SCMC molecules exhibit strong ability to drive water molecules on calcite surface. The binding energy between three calcite surfaces and SCMC from strong to weak follows the order: (1‐10) > (104) > (110). [ABSTRACT FROM AUTHOR]

By performing a molecular dynamics simulation, fragmentation of Cun clusters scattering from a single-crystal Cu (111) surface is studied. The interactions among copper atoms are modeled by tight-binding potential, and the positions of the copper clusters at each time step are calculated by integrating the Newton equations of motion. The percentage of unfragmented clusters depends on the incident velocities, angles of incidence, and surface structure. The influence of surface structure on the fragment distribution is discussed, and the clusters appear to be more stable under an axial channeling condition. The fragment distribution shifting toward the small fragment range for cluster scattering along a random direction is confirmed, indicating that the cluster undergoes more intensive fragmentation. [ABSTRACT FROM AUTHOR]