Lennard-Jones Potential Research Articles

Development of accurate potentials for the physisorption of water on graphene.

From coupled-cluster singles and doubles model including connected triples corrections [CCSD(T)] calculations on the water dimer and B97D/CC on the water-circumcoronene complex at a large number of randomly generated conformations, interaction potentials for the physisorption of water on graphene are built, accomplishing almost sub-chemical accuracy. The force fields were constructed by decomposing the interaction into electrostatic and van der Waals contributions, the latter represented through improved Lennard-Jones potentials. Besides, a Chemistry at Harvard Macromolecular Mechanics (CHARMM)-like term was included in the water-water potential to improve the description of hydrogen bonds, and an induction term was added to model the polarization effects in the interaction between water and polyaromatic hydrocarbons (PAHs) or graphene. Two schemes with three and six point charges were considered for the interactions water-water and water-PAH, as Coulomb contributions are zero in the water-graphene system. The proposed fitted potentials reproduce the ab initio data used to build them in the whole range of distances and conformations and provide results for selected points very close to CCSD(T) benchmarks. When applied to the water-graphene system, the obtained results are in excellent agreement with p-CCSD(T), revised symmetry-adapted perturbation theory based on density functional theory monomer properties (DFT-SAPT), and diffusion Monte Carlo reference values. Furthermore, the stability of the various conformers water-PAH and water-graphene, as well as the different trends observed between these systems are rationalized in terms of the modifications of the electrostatic contribution.

Incorporating ion-specific van der Waals and soft repulsive interactions in the Poisson-Boltzmann theory of electrical double layers.

Electrical double layers (EDLs) arise when an electrolyte is in contact with a charged surface, and are encountered in several application areas including batteries, supercapacitors, electrocatalytic reactors, and colloids. Over the last century, the development of Poisson-Boltzmann (PB) models and their modified versions have provided significant physical insight into the structure and dynamics of the EDL. Incorporation of physics such as finite-ion-size effects, dielectric decrement, and ion-ion correlations has made such models increasingly accurate when compared to more computationally expensive approaches such as molecular simulations and classical density functional theory. However, a prominent knowledge gap has been the exclusion of van der Waals (vdW) and soft repulsive interactions in modified PB models. Although short-ranged as compared to electrostatic interactions, we show here that vdW and soft repulsive interactions can play an important role in determining the structure of the EDL via the formation of a Stern layer and in modulating the differential capacitance of an electrode in an electrolyte. To this end, we incorporate ion-ion and wall-ion vdW attraction and soft repulsion via a 12-6 Lennard-Jones (LJ) potential, resulting in a modified PB-LJ approach. The wall-ion LJ interactions were found to have a significant effect on the electrical potential and concentration profiles, especially close to the wall. However, ion-ion LJ interactions do not affect the EDL structure at low bulk ion concentrations (<1 M). We also derive dimensionless numbers to quantify the impact of ion-ion and wall-ion LJ interactions on the EDL. Furthermore, in the pursuit of capturing ion-specific effects, we apply our model by considering various ions such as Na, K+, Mg2+, Cl-, and SO42-. We observe how varying parameters such as the electrolyte concentration and electrode potential affect the structure of the EDL due to the competition between ion-specific LJ and electrostatic interactions. Lastly, we show that the inclusion of vdW and soft repulsion interactions, as well as hydration effects, leads to a better qualitative agreement of the PB models with experimental double-layer differential capacitance data. Overall, the modified PB-LJ approach presented herein will lead to more accurate theoretical descriptions of EDLs in various application areas.

Catalytic effect of graphene on the inversion of corannulene using a continuum approach with the Lennard-Jones potential.

The catalytic effect of graphene on the corannulene bowl-to-bowl inversion is confirmed in this paper using a pair-wise dispersion interaction model. In particular, a continuum approach together with the Lennard-Jones potential are adopted to determine the interaction energy between corannulene and graphene. These results are consistent with previous quantum chemical studies, which showed that a graphene sheet reduces the barrier height for the bowl-to-bowl inversion in corannulene. However, the results presented here demonstrate, for the first time, that the catalytic activity of graphene can be reproduced using pair-wise dispersion interactions alone. This demonstrates the major role that pair-wise dispersion interactions play in the catalytic activity of graphene.

Single-wall boron nitride nanotubes encapsulating conjugated bithiophene molecule: Raman analysis

In this paper, we investigate the hybrid systems based on single-wall boron nitride nanotubes (SWBNNTs) encapsulating the bithiophene molecule (2T) by a combination of molecular dynamics, density functional theory (DFT), and spectral moments method (SMM). The structural stability of the hybrid systems 2T@SWBNNTs is explored using Lennard-Jones potential. We computed the optimal SWBNNTs diameter for which the resulting hybrids 2T@SWBNNTs are stable. Then, we report the calculated Raman spectra of the 2T molecule and the (7,7) SWBNNT before and after encapsulation. The structural stability and the occurrence (or not) of a possible charge transfer in the hybrid 2T@ (7,7) are investigated by analyzing the encapsulation effects on the Raman active modes of the (7,7) nanotube, as well as on those of the 2T molecule.

A transferable double exponential potential for condensed phase simulations of small molecules.

The Lennard-Jones potential is the most widely-used function for the description of non-bonded interactions in transferable force fields for the condensed phase. This is not because it has an optimal functional form, but rather it is a legacy resulting from when computational expense was a major consideration and this potential was particularly convenient numerically. At present, it persists because the effort that would be required to re-write molecular modelling software and train new force fields has, until now, been prohibitive. Here, we present Smirnoff-plugins as a flexible framework to extend the Open Force Field software stack to allow custom force field functional forms. We deploy Smirnoff-plugins with the automated Open Force Field infrastructure to train a transferable, small molecule force field based on the recently-proposed double exponential functional form, on over 1000 experimental condensed phase properties. Extensive testing of the resulting force field shows improvements in transfer free energies, with acceptable conformational energetics, run times and convergence properties compared to state-of-the-art Lennard-Jones based force fields.

Development of a program for mathematical modeling of molecular dynamics processes

The paper presents the results of developing a program for mathematical modeling of molecular dynamics processes in crystal structures using the MatLab software package. The theoretical part describes the differential equations for simulation, their initial and boundary conditions, and the difference approximation. A method was chosen based on the principle of modeling molecular dynamics using one of the pair potentials, namely the Lennard-Jones potential. In the practical part, the chaotic motion (migration) of atoms in 2D and 3D crystal lattices has been simulated. The distribution over the computational cell and the migration of atoms beyond its limits are shown. The dependence between the bound energies in real metals and the computational model has been determined. The potential of interaction has been determined, which turns out to be positive. The developed program showed high accuracy of simulation results, as well as higher speed compared to other similar programs for molecular dynamics simulation.

Collective behavior of passive and active circle swimming particle mixtures.

We present a numerical study on a binary mixture of passive and circle swimming, self-propelling particles which interact via the Lennard-Jones (LJ) potential in two dimensions. Using Brownian Dynamics (BD) simulations, we present state diagrams using the control parameters such as attraction strength, angular velocity, self-propulsion velocity and composition. In a symmetric mixture, the system undergoes a transition from a mixed gel to a rotating passive cluster state and finally to a homogeneous fluid state as translational activity increases. The formation of the rotating cluster of passive particles surrounded by active and passive monomers is attributed to the combined effect of composition, activity and strength of attraction of the active particles. Different phases are characterized using radial distribution functions, bond order parameters, cluster fraction and probability distribution of local volume fractions. The present study addresses comprehensively the intricate role of activity, angular velocity, inter-particle interaction and compositional variation on the phase behavior. The predictions presented in the study can be experimentally realized in synthetic colloidal swimmers and motile bacterial suspensions.

NMR spectroscopy to study cyclodextrin-based host-guest assemblies with polynuclear clusters.

Natural cyclodextrin (CD) macrocycles are known to form diverse inclusion complexes with a wide variety of organic molecules, but recent work has revealed that inorganic clusters also form multicomponent supramolecular complexes and edifices. Such molecular assemblies exhibit a high degree of organization in solution governed by various chemical processes including molecular recognition, host-guest attraction, hydrophobic repulsion, or chaotropic effect. Nuclear magnetic resonance (NMR) spectroscopy is one of the most efficient and practical analytical techniques to characterize the nature, the strength and the mechanism of these interactions in solution. This review provides a brief overview on recent examples of the contribution of NMR to the characterization of hybrid systems in solution based on CD with polynuclear clusters, including polyoxometalates (POMs), metallic clusters and hydroborate clusters. The focus will be first on using 1H (and 13C) NMR of the host, i.e., CD, to identify the nature of the interactions and measure their strength. Then, 2D NMR methods will be illustrated by DOSY as a means of highlighting the clustering phenomena, and by NOESY/ROESY to evidence the spatial proximity and contact within the supramolecular assemblies. Finally, other NMR nuclei will be selected to probe the inorganic part as a guest molecule. Attention will be paid to classical host-guest complexes Cluster@CD, but also to hierarchical multi-scale, multi-component assemblies such as Cluster@CD@Cluster.

Automating the generation of detailed kinetic models for halocarbon combustion with the Reaction Mechanism Generator

Originally developed to predict the chemical kinetics of hydrocarbon combustion via automated generation of detailed reaction mechanisms, Reaction Mechanism Generator (RMG) contains extensive thermokinetic data for C,H,O chemisty, and has more recently been expanded to nitrogen and sulfur. In this work, we present the addition of halogen (fluorine, chlorine, and bromine) chemisty to RMG to enable automated generation of detailed kinetic models for halocarbon combustion. RMG’s existing reaction templates are updated to include halogens, and 11 new reactions families are created specific to halogen chemistry. Notably, kinetics for more than 1000 elementary reactions are calculated via ab inito methods and transition state theory, and these kinetic data are combined with kinetics from literature sources to train rate rule decision tree estimators. Additionally, halogen groups are added to RMG’s statistical mechanics database, enabling model generation with RMG’s pressure dependence module and automated computation of microcanonical rate constants for unimolecular networks. Halogen groups are also incorporated in RMG’s transport database to provide estimated parameters for the Lennard-Jones potential, important for transport-dependent simulations including laminar flame speeds. To demonstrate RMG’s capability for predicting halocarbon combustion, RMG is used to build a flame suppression model for 2-BTP (CH2=CBrCF3) in methane flames. The laminar flame speeds of RMG’s 2-BTP model show good agreement with a published model under a variety of reaction conditions. Automating the generation of detailed kinetic models for halocarbon combustion will facilitate the exploration of previously unexplored reaction pathways, thereby accelerating the development of greener refrigerants and suppressants, as well as advancing the field of automated mechanism generation.

A revised Lennard-Jones potential for bubble nucleation study of argon based on the molecular dynamics simulation method

Bubble nucleation in boiling heat transfer is a microscale phenomenon, which is usually investigated by the molecular dynamics simulation method with the study object of argon. The simple potential model of argon favors revealing the bubble nucleation mechanism. However, the published works indicate that the required heating temperature for achieving bubble nucleation inside liquid argon is unreasonable and usually over the critical temperature. Therefore, in this study, a revised Lennard-Jones (L-J) potential for bubble nucleation study of argon is proposed based on the “PK” norm that bubble nucleation happens when the average kinetic energy of a group of liquid atoms exceeds their potential barrier (absolute value of atomic potential energy). The parameters α and β are added to the original L-J potential to weaken the phase transition barrier and reduce atomic balance distance, corresponding to the functions of lowering onset nucleation temperature and avoiding the unreasonable change of liquid argon properties, respectively. Besides, a moving top wall based on the force balance is conducted to maintain the simulation system pressure at the expected value. Simulation results indicate that based on the revised L-J potential and pressure controlled at one atmosphere, only the evaporation phenomenon happens when the heat source temperature is fixed at 85 K within the simulation time of 10 ns, while it converts into the bubble nucleation phenomenon as the thermostat temperature is raised to 90 K, which is very close to the onset boiling temperature of liquid argon (87.2 K). In addition, the relative differences between the original and revised potentials in the density, thermal conductivity, and thermal diffusion coefficient are 1.31%, 33.50%, and 233.33%, respectively. The difference in the third property is significant, but compared with the benchmark value obtained by the popular property database RefProp, the computational accuracy of the revised potential is higher than the original potential. Hence, the revised L-J potential is more suitable for the bubble nucleation study of argon by using the molecular dynamics simulation method.

A new correlation model for predicting the melting and boiling temperatures of the Lennard-Jones systems

The Lennard-Jones (LJ) potential function is widely employed in molecular dynamics simulations. In this study, the LJ potentials under different characteristic diameter σ and characteristic energy ε were simulated, and the changes in properties such as number density, total energy, phase transition latent heat, and phase transition temperature were detailed. With the increase of σ, the melting and boiling temperatures of the LJ systems and the thermodynamic temperature range corresponding to liquid decrease, while with the increase of ε, the melting and boiling temperatures and the thermodynamic temperature range of liquid increase. Moreover, the phase transition latent heat hardly changes with the increase of σ, but significantly increases with ε. The number densities at the melting and boiling temperatures are only dependent on σ, and are not nearly influenced by ε. Furthermore, based on a modified Lindemann’s melting criterion, a new empirical correlation model is proposed to predict the melting and boiling temperatures of the LJ systems, where the phase transition points are in good agreement with the experimental values. For the melting point, the absolute error between the formula and the experimental measurement for inert gas and methane is no more than 10 K, and for the boiling point, the absolute error is less than 15 K. By this new presented model, some thermophysical properties of the LJ potential systems can be quickly obtained and evaluated.

Collision integrals and viscosity coefficients of argon–carbon thermal plasmas: Comparison using different interaction potentials

The calculated values of collision integrals of the majority of binary interactions that can be involved in argon/carbon (Ar/C) plasmas are presented in this work. The studied plasmas are considered to be in local thermodynamic equilibrium, and calculations are performed from 1000 to 30 000 K. Computations have been carried out first for standard potentials and second for the Improved Lennard-Jones (ILJ) potential. In this paper, a clear and well detailed report is given for each methodology adopted to calculate the omega integrals, together with the main data needed to perform these computations. The obtained values of collision integrals have been compared with some data reported in the literature, and then, they are used to estimate the viscosity of two plasma systems, namely, pure argon and a mixture of argon and carbon (Ar/C). The calculation of viscosity coefficients is made on the basis of the Chapman–Enskog method and developed to the first approximation. The important contribution of the charge exchange process and its influence on the accuracy of the diffusion-type collision integrals of neutral–parent ion systems are emphasized. Although some discrepancies are observed, comparisons of our results with those of previously published studies show an overall satisfactory agreement in most of the cases. Our investigation of the data uncertainty further confirms the suggestion that the ILJ approach is an excellent candidate to provide collision integrals with acceptable accuracy when reliable experimental data or accurate theoretical calculations are unavailable. For that, all the necessary collision integrals needed to calculate reliable transport properties of the Ar/C plasma mixtures are reported in this work.

Construction the hierarchical architecture of molybdenum disulfide/MOF composite membrane via electrostatic self-assembly strategy for efficient molecular separation

• Electrostatic LBL self-assembly strategy is firstly employed to integrate MoS 2 with CMOF. • Superior rejection rates are increased above 27–55% more than that of monomer membranes for FQs. • Synergy of size exclusion, electrostatic repulsion, and hydrophilic interaction is explained. • High stability in harsh environments for 72 h and over 90% rejection against FQs in the real sample. Developing a novel nanofiltration membrane for effectively purifying antibiotic wastewater has been a daunting challenge in recent years. However, a convenient and controllable strategy for constructing membranes with two-dimensional nanomaterials (2DNMs) and metal–organic frameworks (MOFs) needs to be further studied. Herein, a loosely hierarchical architecture composite membrane has been fabricated, utilizing an electrostatic layer-by-layer (LBL) self-assembly method to intercalate chitosan crosslinked UiO-66-NH 2 MOFs (CMOF) into MoS 2 laminates. Through regulating the CMOF content, lower hydraulic-resisted channels and precise separation regions have been formed in the hierarchical architecture. The well-designed MoS 2 /CMOF composite membrane exhibited enhanced water permeance (78.98 ± 1.45 L·m -2 h −1 bar −1 ) and superior antibiotic rejection capability (98.01 ± 1.12% for ciprofloxacin and 94.31 ± 0.68% for ofloxacin), which are increased by 27–55% more than monomer membranes. Detailed analysis results indicate the nanofiltration performance of the MoS 2 /CMOF composite membrane depends heavily on the synergistic mechanism, including the molecular sieving effect (size exclusion), electrostatic repulsion, and hydrophilic-hydrophobic interaction. Besides, the MoS 2 /CMOF composite membrane has emerged with excellent antifouling ability and long-term stability, which could maintain favorable rejection efficiency in continuous nanofiltration for 72 h under an alkaline and acidic environment. Furthermore, it presents over 90% antibiotic rejection rates for real water samples obtained from the municipal domestic sewage and livestock wastewater along the Xiangjiang River in China, indicating its good availability. In general, this work provides a new vision and a reasonable design strategy to construct 2DNMs/MOFs-based nanofiltration membranes with hierarchical architecture, further expanding their application in wastewater treatment and reclamation, in harmony with the global trend of green and low-carbon development.

Contact-based molecular dynamics of structured and disordered proteins in a coarse-grained model: Fixed contacts, switchable contacts and those described by pseudo-improper-dihedral angles

We present a coarse-grained Cα-based protein model that can be used to simulate structured, intrinsically disordered and partially disordered proteins. We use a Go-like potential for the structured parts and two different variants of a transferable potential for the disordered parts. The first variant uses dynamic structure-based (DSB) contacts that form and disappear quasi-adiabatically during the simulation. By using specific structural criteria we distinguish sidechain-sidechain, sidechain-backbone and backbone-backbone contacts. The second variant is a non-radial multi-body pseudo-improper-dihedral (PID) potential that does not include time-dependent terms but requires more computational resources. Our model can simulate in reasonable time thousands of residues on millisecond time scales. Program summaryProgram Title: cgCPC Library link to program files:https://doi.org/10.17632/dp7gwrs94n.1Code Ocean capsule:https://codeocean.com/capsule/9528010Licensing provisions: MITProgramming language: C++ (new version), Fortran (old version)Nature of problem: Simulations of one or more protein chains, structured, intrinsically disordered or partially disordered. Calculating their equilibrium and kinetic properties in processes including but not limited to: folding, aggregation, conformational changes, formation of complexes, aggregation, response to deformation. All those processes need long simulation times or many trajectories to properly sample the system.Solution method: The simulations use a molecular dynamics implicit-solvent coarse-grained model where each pseudoatom represents one amino acid residue. Residues are harmonically connected to form a chain. The system evolves according to Langevin dynamics. The backbone stiffness potential involves bond angle and dihedral angle terms (or a chirality term in the structured case). Residues interact via modified Lennard-Jones or Debye-Hueckel potentials.The potential is different for structured and disordered parts of a protein. A Go model contact map is used for the structured parts, where an interaction between two residues is attractive if effective spheres associated with their heavy atoms overlap in the native structure [1,2,3,4]. Non-attractive contacts use only the repulsive part of the Lennard-Jones potential. The potential for the disordered parts has two versions: in the quasi-adiabatic Dynamic Structure-Based (DSB) variant, the contacts are formed dynamically based on the structure of the chain and are quasi-adiabatically turned on and off [5,6]. In the slower, but more accurate Pseudo-Improper-Dihedral (PID) variant the Lennard-Jones term is multiplied by a pseudo-improper-dihedral term that gives similar geometric restrictions with a time-independent Hamiltonian [7].Proteins can be pulled by their termini to mimic stretching by an Atomic Force Microscope [8,9]. Multiple protein chains can be put in a simulation box with periodic boundary conditions or with walls that may be repulsive or attractive for the residues. The walls may move to mimic pulling or shearing deformations. The program accepts PDB files or protein sequences with optional user-defined contact maps. It saves the results in an output file (summary), a PDB file (structure) and a map file (contact map in a given snapshot).Additional comments including restrictions and unusual features: The program supports openMP (effective up to 8 cores, use 4 cores for optimal speed-up). The C++ version is hosted on Github, the Fortran version is distributed as a .tar archive.

Computer simulation of AlCoCuFeNi high-entropy alloy thin film deposition and crystallization

The processes of deposition and crystallization of high-entropy AlCoCuFeNi alloy thin film on a substrate of silicon (100) are studied by classical molecular dynamics simulation. Total simulation time reaches 50 ns. The embedded atom model is used to describe the interaction among Al–Co–Cu–Ni–Fe. Interaction between the atoms of Al, Co, Cu, Fe, Ni, and the Si substrate is described using the Lennard–Jones potential, and the interaction between the silicon atoms was modeled using the Stillinger–Weber potential. It is found that at the first stage of deposition small clusters are formed and the process of crystallization starts after ~ 5 ns of simulation, at the characteristic sizes of clusters of about 2 nm. At the end of the simulation, after the 50 ns of modeling, the simulated film contains a face-centered cubic phase, a body-centered cubic phase, a hexagonal close-packed phase, and an amorphous phase. An analysis of the radial distribution of atoms makes it possible to determine the distances between the nearest neighbors and estimate the lattice parameters of these phases.

Crystallography of honeycomb formation under geometric frustration

As honeybees build their nests in preexisting tree cavities, they must deal with the presence of geometric constraints, resulting in nonregular hexagons and topological defects in the comb. In this work, we study how bees adapt to their environment in order to regulate the comb structure. Specifically, we identify the irregularities in honeycomb structure in the presence of various geometric frustrations. We 3D-print experimental frames with a variety of constraints imposed on the imprinted foundations. The combs constructed by the bees show clear evidence of recurring patterns in response to specific geometric frustrations on these starter frames. Furthermore, using an experimental-modeling framework, we demonstrate that these patterns can be successfully modeled and replicated through a simulated annealing process, in which the minimized potential is a variation of the Lennard-Jones potential that considers only first-neighbor interactions according to a Delaunay triangulation. Our simulation results not only confirm the connection between honeycomb structures and other crystal systems such as graphene, but also show that irregularities in the honeycomb structure can be explained as the result of analogous interactions between cells and their immediate surroundings, leading to emergent global order. Additionally, our computational model can be used as a first step to describe specific strategies that bees use to effectively solve geometric mismatches while minimizing cost of comb building.

Application of the Lennard-Jones potential for calculating the surface tension and the formation enthalpy of a binary solution

Abstract In our previous work on this topic, the Lennard-Jones potential was used to derive a semi-empirical formula relating the enthalpy of vaporization of a liquid to the density of the liquid and vapour at equilibrium with it, and a very good agreement between the formula and experimental data was demonstrated. In the present work, this approach has been further developed. The purpose of this work was to apply the Lennard-Jones potential to derive a semi-empirical formula describing the dependence of the surface tension of a liquid on temperature, as well as the dependence of the formation enthalpy of a binary solution on its composition. Solution formation was considered as consisting of two stages: 1) removal of x moles of the first component and 1– x moles of the second component from pure liquids into vacuum; in this case, the expended energy is equal to the energy of interaction of these molecules with all molecules in the volume of these liquids in accordance with the Lennard-Jones potential; 2) their movement from vacuum to an infinitely large volume of a solution of composition x; in this case, the released energy is equal to the energy of interaction of these molecules with all the molecules of the solution. The enthalpy of solution formation is equal to the algebraic sum of the mentioned interaction energies. Since surface tension is due to the action of the same forces of intermolecular interaction, a similar formula can be used to describe the dependence of surface tension on temperature. A comparison of the derived equations with the experiment shows that the resulting equations are in exceptionally good agreement with the experimental data.

1D van der Waals heterostructures based on single-walled carbon nanotubes encapsulating linear carbon chains: Stability and charge transfer evidence from Raman spectroscopy

The emerging one-dimensional van der Waals heterostructures (1D vdWHTs) are raising a lot of enthusiasm due to the possibilities for creating novel physical properties. In this paper, we focus on single-walled carbon nanotubes (SWCNTs) encapsulating a series of hydrogen-terminated linear carbon chains (LCCs) of lengths ranging from 4 up to 40 carbon atoms as a template for 1D vdWHTs (LCCs@SWCNTs). We explored the structural properties and stability of the LCCs@SWCNTs systems. The optimal SWCNT diameter for which the resulting 1D vdWHTs are stable is determined using Lennard-Jones (LJ) potential. SWCNTs with diameters of around 0.75 nm are found most convenient to accommodate LCCs. Combining the molecular dynamics (MD), the density functional theory (DFT), bond polarizability model (BPM), and the spectral moment’s method (SMM), we computed the Raman spectra of the free LCCs and LCCs@(6,5) 1D vdWHTs. The stability and charge transfer in the LCCs@(6,5) systems are evinced by analyzing the Raman active modes of the LCCs, as well as the radial breathing mode (RBM) and G-band of the (6,5) SWCNT before and after filling. These findings provide benchmark theoretical data to understand both the Raman data of the LCCs and the confinement effect on those of the SWCNTs encasing LCCs which have not been clearly addressed before.

Enhanced thermophysical properties of water-based single and hybrid metallic nanofluids: Insights from Equilibrium Molecular Dynamics

The effect of single (Cu or Ag) and hybrid (Cu+Ag) metallic nanoparticles on the thermophysical properties, namely viscosity and thermal conductivity of water-based nanofluids, has been studied using Equilibrium Molecular dynamics (EMD) simulation. The TIP3P (three-site transferrable intermolecular potential) water model has been chosen. The interaction of water molecules has been modelled by the Lennard-Jones (L J) potential in combination with Coulomb potential. The embedded-atom (EAM) potential method has been used for hybrid (Cu and Ag) atom interaction. Simulation has been performed at 303 K and atmospheric pressure using the Berendsen algorithm under NVT (constant number, constant volume, and constant temperature) ensemble with production steps of 2 ns and integral step of 1fs. Interestingly, nanofluids containing one metallic nanoparticle (Cu or Ag) have lower thermal conductivity and viscosity than nanofluids having hybrid metallic nanoparticles with the same volume fraction.

Thermodynamic properties of Ar, Kr and Xe from a Monte Carlo-based perturbation theory with an effective two-body Lennard-Jones potential

A third-order perturbation theory is used to obtain the equilibrium properties of Ar, Kr and Xe over wide ranges of temperatures and densities. The theory belongs to the framework of the inverse temperature expansion of the Helmholtz free energy, with the perturbation terms determined from Monte Carlo simulation. The interactions are modeled by an effective two-body Lennard-Jones potential incorporating the main contribution of the three-body interactions. To this end, the ratio of three-body to two-body configuration energies have been determined also from Monte Carlo simulation. The results for the pressure and energy at supercritical temperatures are in quite good agreement with experimental data. The liquid–vapor coexistence is also reproduced fairly well, although for Ar and Kr the critical temperature is slightly overestimated as well as the liquid densities at low temperatures, and the coexistence densities of Xe are slightly overestimated for the vapor and underestimated for the liquid near the critical point. In any case, the calculations show a remarkable improvement in the predicted coexistence curve with including the three-body contribution.