Values Of Self-diffusion Coefficients Research Articles

Molecular dynamics simulation study of sodium ion structure & dynamics in water in ionic liquids electrolytes using 1-butyl-3-methyl imidazolium tetrafluoroborate and 1-butyl-3-methyl imidazolium hexafluorophosphate

In this paper, we have performed an all-atom molecular dynamics simulation to understand the structure and dynamics of Na+ ions in water mixed Ionic liquids (Water in Ionic liquid). Two ionic liquid (IL) systems consist of (1) 1-butyl-3-methylimidazolium [BMIM] tetrafluoroborate [BF4] and (2) 1-butyl-3-methylimidazolium [BMIM] hexafluorophosphate [PF6] were considered in this work. We understand various inter-molecular structures and dynamic and thermodynamic behaviours of Na+ ions in the water-mixed IL systems. The water (H2O) mole fractions (x) varied from 0.33 to 0.71. The neat ILs [BMIM][BF4] and [BMIM][PF6] pairwise radial distribution functions show a decrease with an increase in x. The [BMIM][PF6] exhibits a strong coordination structure with Na+ ions across the entire range of x values. The rdf between the pairs of Na+-[PF6] presents a significant interaction compared to Na+ and [BF4]. The Na + ions manifested greater coordination with H2O In H2O-[BMIM][PF6] compared to H2O-[BMIM][BF4]. The self-diffusion coefficient (D) values of Na + ions increase with the rise in x in both ILs. The D values of Na + ions are 10-fold higher in [BMIM][BF4] than [BMIM][PF6]. The ionic conductivity values are higher for [BMIM][BF4]. Overall, this paper unveils molecular-level insights for understanding the behavior of Na+ ions in the water in ionic liquid systems.

The influence of anions in the ionic liquid-water mixtures on the conformational structures of emeraldine base and emeraldine salt form of polyaniline

The development of antifouling membranes for water filtration applications is challenging. Conducting polymers can show enhanced antifouling characteristics by blending with various polymers, nanomaterials, and Ionic liquids (ILs). In this paper, we perform an all-atom molecular dynamics simulation on a conducting polymer polyaniline (PANI) immersed in IL-water mixtures. Two forms of PANI were considered, namely Emeraldine base (EB) and Emeraldine salt (ES) as well as two different water-mixed ILs are considered namely (a) 1-ethyl-3-methyl imidazolium [EMIM]+ hexafluorophosphate [PF6]- and (b) 1-ethyl-3-methyl imidazolium [EMIM]+ tetra-fluoroborate [BF4]-. We present various intra- and inter-molecular structural properties, solvation thermodynamics, and dynamic properties. We observe that with an increase in IL concentration, the radius of gyration (Rg) value shows a decrease for ES in pure state in both ILs; on the other hand, we see a minimal increase in the Rg values of EB in both ILs. The dihedral angle distribution analysis shows a combination of gauche and trans state for ES, whereas trans state is more pronounced for the case of EB in both water-IL mixtures. The radial distribution function (RDF) analysis between the ortho, meta carbons of the benzene rings, and the amine groups on ES with [BF4]- and [PF6]- show significant structural peaks. On the other hand, EB and ES show lower interaction with the water molecules. The number of hydrogen bonds (h-bonds) between polymer and water is higher for EB than ES in both IL-water mixtures. The hydrogen bond lifetime (τ) values show one-fold higher values for EB than ES. The self-diffusion coefficient (D) values of water show a decrease with an increase in IL concentration. The thermodynamic properties solvation enthalpy (ΔH) and excess molar volume (VmE) for both ES and EB show a more favorable solvation in [EMIM]+[BF4]- when compared to [EMIM]+[PF6]- with an increase in IL concentration. These observations are crucial for selecting ILs and designing sustainable polymers for antifouling membranes.

Computational analysis of anionic dyes adsorption on the kaolinite (001) surface: Combination of quantum chemical calculations and molecular simulation methods

Clay minerals are increasingly used to remove dyes from wastewater. In recent times, computational simulation methods have become indispensable for investigating the adsorption mechanisms of dyes on clay surfaces at the molecular level. This study investigates the adsorption features of two acid dyes, namely acid blue 25 (AB25) and acid red 88 (AR88), on the (001) surface of kaolinite in an aqueous medium using density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD) simulations. Quantum chemical parameters (QCPs) show that the AB25 molecule exhibits higher reactivity compared to the AR88 molecule. As well, analysis of the sigma profile reveals a moderate polarity of the two dye molecules studied in comparison with the water molecule. The low-energy adsorption configuration of AB25 and AR88 molecules show that each molecule is oriented parallel to the (001) surface of kaolinite over short distances. The adsorption energies indicate that the kaolinite (001) surface has high affinity towards AB25 in comparison with the AR88 molecule (Eads(AB25) = -926.01 Kcal.mol−1; Eads(AR88) = -742.08 Kcal.mol−1), which was supported by analysis of the self-diffusion coefficient (SDC) values (SDCAB25 = 7.79 × 10-10 m2.s−1; SDCAR88 = 1.4 × 10-9 m2.s−1). Additionally, calculation of the radial distribution function of the oxygen and nitrogen atoms of AB25 and AR88 molecules show the contribution of these atoms in the chemical interactions that take place with the (001) surface of kaolinite. The adsorption mechanism of the investigated dye molecules may be influenced by both donor–acceptor and van der Waals interactions. The theoretical results from this study could be useful for better understanding the adsorption mechanisms of other acid dyes on clay minerals.

A molecular dynamics simulations study on the modification of aqueous solution structure and dynamics in presence of monovalent salts: An electronic continuum correction approach and effect of ion size

The hydrogen bonding structure and dynamics of water are investigated by varying the concentrations up to 6.18 m for full-charged and the electronic continuum correction with rescaling (ECCR) charged model for NaCl solutions using classical molecular dynamics simulations. We have also considered the seven different (MCl/NaX) salt solutions at 6.18 m with varying monovalent cations (M+) or anions (X-). The first and second solvation shells of water in both full- and ECCR models are affected by NaCl concentrations, and destruction of the tetrahedral network structure is observed. Probability of ion pair formation is higher in KCl and NaF solutions compared to other salts at 6.18 m. The self-diffusion coefficient values of water, Na+ in full-charged, and Cl− in ECCR models are in good agreement with the experimental results. The hydrogen bond lifetime of water does not significantly change with increasing NaCl salt concentrations, but Cl−-water lifetime is significantly lowered in the ECCR model.

Molecular dynamic simulation of the [N(C4H9)4]BF4 / (110) α-Al2O3 interface

The structure and transport properties of the pure salt [N4]BF4 and this salt located in the contact with the (110) surface of a-Al2O3 were studied using a MD computer simulation in order to reveal the effect of the salt/oxide interface on the structure and properties of the salt. The radial distribution functions of the ions and their mean square displacements were analyzed as a function of the temperature during the cooling of the salt. It was found that in all the cases anions are more mobile than cations. The molten phase of [N4]BF4 tends to crystallize at temperature 420 K which is close to the experimental melting point. The salt located in the [N4]BF4/(110)Al2O3 interface exhibits high values of anion self-diffusion coefficients which are higher by 1.2–2 orders of magnitude than in pure salt. This effect is likely to be caused by the formation of a layered atomic structure located within a characteristic thickness of 5 nm. Despite the structuring, the structure of the salt is amorphous, no crystallization-related effect is observed. The results of MD simulations agree with the experimental effect of the conductivity enhancement observed previously in [N4]BF4-Al2O3 nanocomposites.

An eco-friendly chitosan-diethylaminoethyl cellulose composite: In-depth analysis of lead (II) and arsenic(V) decontamination from water with molecular perspectives

Water pollution from heavy metal ions, such as lead (II) and arsenic (V), is a widespread problem that has spurred researchers to look for efficient, environmentally acceptable treatment methods. In this context, the present study explores the potentiality of a novel, low-cost biosorbent material for the efficient removal of these toxic contaminants. A chitosan crosslinked@diethylaminoethyl cellulose (Cs@DEAE-C) composite was synthesized by crosslinking chitosan and diethylaminoethyl cellulose (DEAE-C) and employed to adsorb Pb(II) and As(V) from water. The monolayer adsorption capacity was found to be 218.71 mg/g for Pb(II) and 41.98 mg/g for As(V), respectively while the uptake process involved chemisorption. The adsorption capability of Cs@DEAE-C for As(V) and Pb(II) was decreased when phosphate and nitrate ions were present. Desorption studies demonstrated that Cs@DEAE-C effectively removed As(V) and Pb(II) for up to five adsorption–desorption cycles. Uncross-linked carbonyl (C = O) and hydroxyl (–OH) groups were found to be the main adsorptive sites for Pb(II) uptake, whereas uncross-linked hydroxyl (–OH) and –NH2 groups were found to be crucial for As(V) absorption. The self-diffusion coefficient values from molecular dynamics (MD) simulation revealed that electrostatic interactions hinder the mobility of metal ions limiting their diffusion ability. This study highlights the efficiency of the low-cost chitosan composite for contaminant removal and suggests its potential applicability in treating real wastewater for other pollutants. Further research could focus on optimizing the synthesis process and exploring the composite's efficacy for additional contaminants.

Self-Organization of Fullerene Derivatives in Solutions and Biological Cells Studied by Pulsed Field Gradient NMR.

Fullerene derivatives are of great interest in various fields of science and technology. Fullerene derivatives are known to have pronounced anticancer and antiviral activity. They have antibacterial properties. Their properties are largely determined by association processes. Understanding the nature and properties of associates in solvents of various types will make it possible to make significant progress in understanding the mechanisms of aggregation of molecules of fullerene derivatives in solutions. Thus, this work, aimed at studying the size and stability of associates, is relevant and promising for further research. The NMR method in a pulsed field gradient was used, which makes it possible to directly study the translational mobility of molecules. The sizes of individual molecules and associates were calculated based on the Stokes-Einstein model. The lifetime of associates was also estimated. The interaction of water-soluble C60 fullerene derivatives with erythrocytes was also evaluated. The values of self-diffusion coefficients and the lifetime of molecules of their compounds in cell membranes are obtained. It is concluded that the molecules of fullerene derivatives are fixed on the cell surface, and their forward movement is controlled by lateral diffusion.

Grain Boundary Grooving by Surface Diffusion in Nickel Bicrystals

Surface self-diffusion was investigated via thermal grooving experiments on nickel bicrystals in combination with numerical simulations of the groove profiles. The objective of this work was the clarification of the dominant mechanism of grain boundary grooving in nickel at T=750∘C and the determination of the respective diffusion coefficients with high accuracy. The literature values of surface self-diffusion coefficients in nickel exhibit high scatter most likely associated with adsorption of impurities, which makes a comparison between different sets of data impractical and drawing conclusions about surface diffusion anisotropy impossible. In this work, thermal grooving experiments were performed on nickel bicrystals with different grain boundary and surface orientations at T=750∘C in forming gas. The groove profiles were measured by means of atomic force microscopy. Surface diffusion was clearly identified as the dominant mechanism of grain boundary grooving. Asymmetrical grain boundary grooving by surface diffusion was modelled numerically. From the comparison of simulated and measured groove profiles, the surface diffusion coefficients were determined with high accuracy and for the first time the anisotropy of surface diffusion was quantitatively measured. The surface self-diffusion in nickel is highly anisotropic, varying between DS=0.3×10−21 m3/s and DS=12.0×10−21 m3/s, whereby the surface diffusion near {100} surfaces is an order of magnitude slower than near {110} and {111} surfaces. The present work demonstrates that thermal grooving is an excellent tool to study the surface diffusion and to determine the respective diffusion coefficients with high accuracy from the comparison of simulated and measured groove profiles.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

Thermodynamic and transport properties of amoxicillin

We have carried out MD simulations of amoxicillin, a drug molecule used as antibacterial agent, in water and ethanol to study thermodynamic properties like solvation free energy and transport phenomena like diffusion, viscosity. The free energy of solvation of amoxicillin in water and ethanol have been estimated at 310 K using thermodynamic integration (TI) and free energy perturbation (FEP) based methods. It has been obtained that the free energy of solvation of amoxicillin in water is higher by ≈ 105 kJ/mol in TIP3P model than in ethanol. We have also reported the solvent accessible surface area (SASA) of solute as well as the hydrogen bonds between solute and solvent for different solvents. The analysis of SASA and hydrogen bond provides more insight on effect of solvent environment in solvation process of amoxicillin. We have also estimated the diffusion coefficient and our results show that diffusion coefficients of amoxicillin depends on solvent environment, as expected, and it is higher in water than that of ethanol. Also, applying the idea of system size dependence of diffusion coefficient, the viscosity coefficient of water and solution of amoxicillin in water have also been estimated. Furthermore, the effects of temperature on diffusion has been studied. The estimated values of self-diffusion coefficients of water are in good agreement with previously reported experimental data within ≈13.5%.

Molecular Dynamics Simulation on the Interaction between Palygorskite Coating and Linear Chain Alkane Base Lubricant

Molecular dynamics (MD) simulations were conducted to investigate the interactions between a palygorskite coating and linear chain alkanes (dodecane C12, tetradecane C14, hexadecane C16, and octadecane C18), representing base oils in this study. The simulation models were built by placing the alkane molecules on the surface of the palygorskite coating. These systems were annealed and geometrically optimized to obtain the corresponding stable configurations, followed by the analysis of the structural changes occurring during the MD process. The interfacial interaction energies, mean square displacements, and self-diffusion coefficients of the systems were evaluated to characterize the interactions between base lubricant molecules and palygorskite coating. It was found that the alkanes exhibited self-arrangement ability after equilibrium. The interfacial interaction was attractive, and the electrostatic energy was the main component of the binding energy. The chain length of the linear alkanes had a significant impact on the intensity of the interfacial interactions and the molecular diffusion behavior. Moreover, the C12 molecule exhibited higher self-diffusion coefficient values than C14, C16 and C18. Therefore, it could be the best candidate to form an orderliness and stable lubricant film on the surface of the palygorskite coating. The present work provides new insight into the optimization of the structure and composition of coatings and lubricants, which will guide the experimental development of these systems for practical applications.

Salt ions induced transport properties of poly(methacrylic acid) PMA in aqueous solutions studied by molecular dynamics simulations

Abstract The detailed atomistic molecular dynamics simulations studies of multiple chain anionic polyelectrolyte poly(methacrylic acid) PMA was carried out to investigate the effect of monovalent salt i.e. NaCl on the transport properties such as self-diffusion coefficient of PMA, salt-ions and water molecules in dilute aqueous solutions. The concentration of NaCl was varied from dilute (0.01 M) to concentrated regime (1 M) and the self-diffusion coefficient of PMA, salt-ions and water molecules were calculated. The self-diffusion coefficient of PMA decreases with increase in NaCl concentration in agreement with experiments and previous reported simulations works. The salt ions i.e. Na+ and Cl- too shows a decrease in their self-diffusion coefficient values with NaCl concentration. The self-diffusivity of water molecules was found to be decrease in a linear manner with salt concentration. The salt-ions exhibits faster movement as compared to PMA and water on account of a higher self-diffusion coefficient.

Effects of concentration and pressure on the aqueous solvation structure of ammonia and composition dependent ion solvation scenario in water-ammonia mixtures

The hydrogen bonding structure of water and its dynamics in aqueous ammonia solution is investigated by using classical molecular dynamics simulations. We have considered eight different mole-fraction of ammonia, ranging from xNH3 = 0.02 to 0.30, and the pressure variation is carried out on the concentrated ammonia solution (xNH3=0.30), ranging from P = 0.1 MPa to 800 MPa, at 293K. The radial distribution function indicates that the addition of ammonia facilitates the structural organization of water, which is further supported by increasing values of asphericity parameter. But, the tetrahedral order parameter values suggest an angularly disordered arrangement of water molecules. The self-diffusion coefficient values of water pass through shallow minima, whereas it increases for ammonia with ammonia concentration in the solution. The application of pressure causes a sharp decline in translation mobility of ammonia compared to water, but at very high pressure (above 600 MPa), both the species diffuse at the same rate. The rotational relaxation of ammonia is approximately three times faster than water in the solution, which further increases along with concentration as well as pressure. A similar trend is also observed in the case of structural reorganization of water-water and water-ammonia hydrogen bonds. The water-water and water-ammonia hydrogen-bond lifetimes are increasing with ammonia concentration, whereas it passes through shallow maxima with the application of pressure. In this study, we have compared two different Lennard-Jones (LJ) combination rule, which causes negligible differences in the calculated properties. The solvation scenario of different ionic (Na+, Cl−) and neutral (Cl0) solutes are also analyzed along with the coordination number. It is observed that the hydration shell of ion is mainly dominated by water molecules in the solution.

Effects of hexamethylenetetramine (HMTA) on the aqueous solution structure, dynamics and ion solvation scenario: A concentration and temperature dependent study with potential HMTA models

The local hydrogen bonding structure of water and its dynamics in hexamethylenetetramine (HMTA) solution is investigated by using classical molecular dynamics simulations. In this study, we have compared two potential HMTA models with different Lennard-Jones (L-J) combination rules. We have considered five different concentrations of HMTA, ranging from pure water to 6.181 m HMTA at 298 K, whereas to calculate the temperature dependence from 298 K to 353 K, we have used 4.187 m concentration of HMTA. From the radial distribution function, it is observed that the addition of HMTA facilitates structural making of water, whereas our calculated values of the tetrahedral order parameter and asphericity of water suggests disordered structure with increasing HMTA concentration. Also there is a significant development of self-aggregation among water and HMTA molecules at higher concentration of HMTA. The self-diffusion coefficient values of water and HMTA is found to be decreased with increasing HMTA concentration in the solution, whereas at concentrations below 1.0 m, it matches well with the experimental observations. Our calculated activation energy of diffusion for HMTA (4.10 ± 0.2 kcal/g mol for Model-II), is very close to the experimental observation (4.34–4.44 kcal/g mol). The structure of the hydration shell of ions of different charges and sizes is also investigated in the presence of HMTA. For all the models, it is observed that the structural and dynamical properties of water and the hydration shell of ion shows negligible difference with varying concentration and temperature. In contrast, the ion−HMTA correlations are model dependent. It is suggested that the HMTA model-I (AM) is the suitable model for representing ion-solvation structure and dynamics particularly at lower concentrations of aqueous-HMTA solution.

Supramolecular structure vs. rheological properties: 1,4–Butanediol at room and elevated temperatures

Hypothesis: The molecular hydrogen-bonding process in liquids with relatively small molecules, like butan-1,4-diol (BDO), results in interesting molecular-aggregation phenomena. These are reflected in a supramolecular self-assembly type of structure that is also expected to importantly influence the rheological properties of the system. The combination of experimental and theoretical methods should be able to reveal such influences in the important feedstock chemical BDO at low and moderate temperatures and further provide an application of the verified BDO model for a theoretical study of the structure at higher temperatures, for which serious health hazards make extensive experimental studies difficult.Experiments: BDO was studied in the temperature range between 25 and 225 °C utilizing the experimental small- and wide-angle x-ray scattering method, molecular dynamics simulations, and the ‘complemented-system approach’.Findings: The theoretical results were experimentally verified and revealed important novel temperature-dependent structure and viscosity-related information, e.g., on aggregate sizes and self-diffusion coefficients, that would remain hidden in purely experimental studies. BDO has diverse applicability in many fields of research and industry, where it is often exposed to high temperatures. Using an experimentally verified model we were able to calculate reliable viscosity and self-diffusion coefficient values for the BDO molecules under such conditions.

Effect of CO2 and H2O on the behavior of shale gas confined inside calcite [104] slit-like nanopore: a molecular dynamics simulation study.

The effect of CO2 and H2O on the behavior of shale gas confined in calcite [104] slit-like nanopore is investigated using molecular dynamics simulation technique. The study is relevant as the advancement of enhance gas recovery (EGR) technologies requires in-depth atomistic understanding of the hydrocarbons, water, carbon dioxide, and other fracturing fluid constituents inside the nanopores of shale gas reservoirs. We are considering carbon dioxide (CO2) because it is an attractive displacing agent for enhanced gas recovery and has the potential to be an "exotic" fracturing fluid. Water (H2O) is considered as it is the major component of water-based fracturing fluids. The structural and dynamical properties of the confined species are computed. The results indicate that the presence of CO2 and H2O in the nanopore drastically affects the behavior of shale gas. The shale gas molecules that were tightly packed near the pore wall displaced towards the center by CO2 and H2O molecules. A new layer of carbon dioxide and water is formed near the pore wall. Further investigation reveals that CO2 molecules align themselves flat near the surface, whereas H2O molecules have directional orientation with oxygen atoms of water molecules pointing towards to wall. The predicted lateral (in-plane) self-diffusion coefficient values of methane, ethane, carbon dioxide and water indicate complex dynamics inside the pore. The investigation shows the fastest dynamics for methane gas followed by ethane. Both CO2 and H2O are almost immobile. The increase in temperature in the range from 300 to 450K does not appear to have any significant impact on the behavior of the molecules inside the pore. The adsorption energies show that both CO2 and H2O have stronger interactions with calcite [104] surface than shale gas molecules. Graphical abstract TOC- Shale gas extraction process is shown on the left side. In the right side is a calcite [104] nanopore (H = 2.2nm) filled with shale gas and fracking chemicals.

Transport properties of zwitterion glycine, diglycine, and triglycine in water

Diffusion, transport of mass in response to concentration and thermal energy gradient, is an important transport property, vital in material science and life science. In the present work, we have studied about the diffusion of zwitterion glycine, zwitterion diglycine and zwitterion triglycine in SPC/E model of water using classical molecular dynamics. Self and binary diffusion coefficients of aqueous solution of these molecules have been estimated using Einstein’s method. Our results agree with experimental data reported in literatures. Temperature dependency of diffusion of glycine in water has been explored using estimated values of self and binary diffusion coefficients at four different temperature. Effects of peptide bond formation in diffusion has been studied using peptide chain composed of up to three monomers of glycine. The system-size dependence of diffusion coefficient has been studied and the shear viscosity of solvent and system has been calculated. Also, the diffusion coefficient of zwitterion glycine in other water model TIP4P/2005 has been estimated. The structure of the system has been analyzed using radial distribution function of different atoms.

Lipid lateral self-diffusion drop at liquid-gel phase transition.

A drop of lipid lateral self-diffusion coefficient at the liquid-gel phase transition in lipid membranes is calculated. So far this drop was missing theoretical description. Our microscopic model captures so-called subdiffusion regime, which takes place on 1 ps-100 ns timescale and reveals a jump of self-diffusion coefficient. Calculation of the jump is based on our recent study of liquid-gel phase transition. Subdiffusive regime is described within the free volume theory. Calculated values of self-diffusion coefficient are in agreement with quasielastic neutron scattering measurements. Self-diffusion coefficient is found to be composed of two factors: one is related to an area per lipid change at the phase transition, and the other one is due to an order of magnitude change in the stiffness of entropic repulsive potential.

Investigating the effects of vacancies on self-diffusion in silicon clusters using classical molecular dynamics.

Due to recent advances in the field of microelectronics, the growth in microelectronics applications, and the exponentially increasing demand for microelectronic devices in the power sector, it is important to study the behavior of silicon at the nanoscale, given that nanoclusters of silicon could be used to design a new kind of lithium-ion batteries with strongly enhanced performance. Here, molecular dynamics was employed to calculate the self-diffusion coefficients of silicon clusters at room temperature and at a temperature approaching the melting point of silicon, complementing experimental efforts in this field. Silicon clusters of the same spherical geometry and size but with different vacancy fractions were studied using molecular dynamics using the Tersoff potential in order to estimate phase changes and self-diffusion coefficients. At 300K, the self-diffusion coefficient was found to vary non-monotonically: the self-diffusion coefficient at a vacancy fraction of 7.5% is half than the vacancy at a fraction of 0%, while the self-diffusion coefficient at a vacancy fraction of 20% is two orders of magnitude larger than that at a vacancy fraction of 0%. However, there is only a marginal monotonic increase in the self-diffusion coefficient values with vacancy fraction at 2000K. The results of this investigation of vacancy-mediated self-diffusion could aid attempts to improve diffusion control, which is crucial to nanocluster applications in various devices, and the results also provide insight into how the temperature, energy, pressure, and phase changes of the silicon clusters depend on vacancy fraction. This may ultimately allow the design and selection of materials for thermoelectric and optoelectronic devices and thermal transducers to be optimized. Our results also indicated that the findings we obtained for the clusters are independent of the particular random vacancy distribution considered and the heating rate applied to the clusters. Graphical Abstract Silicon nanoparticles (SNP) are among the best options to choose from for the design of devices for renewable energies; SNP based material performance can be effectively tailored by controling the vacancy, temperature and other properties of the SNP.

Transport properties of methane, ethane, propane, and n-butane in water

In this work, we have estimated self diffusion coefficients along with the binary diffusion coefficients of mixtures of alkane (methane, ethane, propane and n-butane) in SPC/E water(H2O). Molecular dynamics study of a binary mixture of alkane gas and SPC/E water, with alkane as solute and water as solvent, have been carried out at different temperatures ranging from 283.15 K to 333.15 K. We have taken a dilute solution of 3 alkane (methane, ethane, propane and n-butane) molecules and 971 water molecules in a system. The role of interaction in the structure of the constituents of the system as a function of temperature is studied with the help of the radial distribution function (RDF) and the coordination numbers. The self-diffusion coefficient of the constituents of the mixture was calculated by using mean square displacement (MSD) and the binary diffusion coefficients of alkane in water have been calculated by using Darken’s relation. The results are then compared with the available experimental values. The values of self-diffusion coefficients of water from the present work come in good agreement with the experimental values within 9% error. The binary diffusion coefficients of ethane, methane, propane and n-butane lie in between the previous experimental values performed by Wise and Houghton, and Witherspoon and D. N. Saraf. The estimated values lie within 30% error to each of the previously reported experimental values. The dependence of the diffusion coefficients on temperature is approximated by Arrhenius-type exponential relationship.