Interaction Potential Model Research Articles

A Machine-Learning-Assisted Crystalline Structure Prediction Framework To Accelerate Materials Discovery.

Modern crystal structure prediction methods based on structure generation algorithms and first-principles calculations play important roles in the design of new materials. However, the cost of these methods is very expensive because their success mostly relies on the efficient sampling of structures and the accurate evaluation of energies for those sampled structures. Herein, we develop a Machine-learning-Assisted CRYStalline Materials sAmpling sysTem (MAXMAT) aiming to accelerate the prediction of new crystal structures. For a given chemical composition, MAXMAT can generate efficient crystal structures with the help of a Python package for crystal structure generation (PyXtal) and can quickly evaluate the energies of these generated structures using a well-developed machine learning interaction potential model (M3GNET). We have used MAXMAT to perform crystal structure searches for three different chemical systems (TiO2, MgAl2O4, and BaBOF3) to test its accuracy and efficiency. Furthermore, we apply MAXMAT to predict new nonlinear optical materials, suggesting several thermodynamically synthesizable structures with high performance in LiZnGaS3 and CaBOF3 systems.

НОВЫЙ ПОДХОД К РАСЧЕТАМ СТОЛКНОВЕНИЯ ЭЛЕКТРОНА С МОЛЕКУЛАМИ

The purpose of the work is to study the mechanism of electron capture by a molecule with the formation of a negative ion. To solve this problem, methods of quantum chemistry are used or other model approaches are used by introducing a certain model interaction potential. The disadvantage of such methods is that for specific molecules we must introduce specific interaction potentials. In this work, we adhere to the standard Coulomb interaction and in a basis in which the kernel of the system of integral equations has a degenerate form.

Modeling of Lane Changing Behavior of Connected Driving Based on Vehicle Interaction Potential

Aiming at the interactive behavior of vehicles changing lanes in the intelligent network traffic environment, the relative position of vehicle, speed, acceleration, and steering angle are introduced to correct the molecular interaction potential, and the vehicle interaction potential model is established. The spatial distribution map of the vehicle interaction potential field under different motion states was drawn, and the changing law of the vehicle interaction potential field was described. By analyzing the longitudinal critical distance of the lane changing safe critical time, the expression of acceptable clearance for lane changing is defined, and the relationship between acceptable clearance and the speed and acceleration of the interactive vehicle is verified by simulation. Combined with the acceptable clearance of lane changing, a lane changing behavior model based on the vehicle interaction potential is established, and the situation of lane changing vehicles subjected to the interaction potential and potential field forces generated by the surrounding vehicles is analyzed, and the driving decision of lane changing vehicles under the action of different potential field forces is given. Compared with the molecular dynamics lane changing model and LS2015 lane changing model, the results show that the vehicle action potential lane changing model can effectively improve the running speed and stability of traffic flow. The research has theoretical significance for the lane changing behavior decisions of networked autonomous vehicles in the future.

Exploration of Stokes hydrodynamic law at molecular length scales.

The celebrated generalized Stokes law predicts that the velocity of a particle pulled through a liquid by an external force, Fex, is directly proportional to the force and inversely proportional to the friction ζ acted by the medium on the particle. We investigate the range of validity of the generalized Stokes law at molecular length scales by employing computer simulations to calculate friction by pulling a tagged particle with a constant force. We thus calculate friction for two model interaction potentials, Lennard-Jones and soft sphere, for several particle sizes, ranging from radius (a) smaller than the solvent particles to three times larger. We next obtain friction from diffusion (D) by using Einstein's relation between diffusion and friction ζ in an unperturbed liquid. We find a quantitative agreement between the two at a small-to-intermediate pulling force regime for all the sizes studied. The law does break down at a large pulling force beyond a threshold value. Importantly, the range of validity of Stokes' scheme to obtain friction increases substantially if we turn off the attractive part of the interaction potential. Additionally, we calculate the viscosity (η) of the unperturbed liquid and find a good agreement with the Stokes-Einstein relation ζ = Cηa for the viscosity dependence with a value of C close to 5 π, which is intermediate between the slip and stick boundary condition.

Virial equation of state for a granular system.

The equation of state for an ideal gas is simple, which is . In the case of imperfect gases where mutual interactions among the constituents are important, pressure P can be expressed as the series expansion of density n with appropriate coefficients, known as virial coefficients . In this paper, we have obtained the first four virial coefficients for a model interaction potential using multidimensional Monte-Carlo integration and importance sampling methods. Next, we perform molecular dynamics simulations with the same for a many-particle system to obtain P as a function of T and n. We compare our numerical data with the virial equation of state.

Scattering of diatomic molecules from graphite

In the last years, state-to-state molecular dynamics simulations of some basic elementary processes, occurring at the gas–surface interface in a wide range of temperatures and collision energies, have been performed by adopting new potential energy surfaces. In this contribution, our attention is mostly addressed to the role of long-range forces, determining the physisorption of gaseous molecules on the surface. Such forces, formulated in terms of the improved Lennard–Jones interaction potential model, control the formation of precursor or pre-reactive state that plays a crucial role in the dynamical evolution of molecules impinging on the surface in the range of low–intermediate collision kinetic energies. The study focuses on the collisions of H2, O2, N2 and CO, initially in their ground and excited vibro-rotational levels, on a graphite surface. The resulting dispersion coefficients, which control the capture of impinging molecules, are compared and found in good agreement with those available in the literature. New selectivity and peculiarities of scattered molecules, crucial to control the kinetics of elementary chemical processes occurring at the gas–surface interfaces under thermal and sub-thermal conditions, of interest in different applied fields, are highlighted.Graphic abstract

Non-Linear Thermophysical Behaviour of Transition Metal Titanium

The propagation of ultrasonic waves in the hexagonal closed packed (hcp) structured lanthanide metal titanium has been investigated in the temperature range 300–1000 K. For this, initially the higher-order elastic constants (second-order elastic constants (SOECs) and third-order elastic constants (TOECs)) were computed using the Lennard-Jones interaction potential model. With the help of SOECs, other elastic moduli such as Young’s modulus (Y), bulk modulus (B), shear modulus (G), Poisson’s ratio (σ) and Pugh’s ratio (B/G) were computed using the Voigt-Reuss-Hill approximation. Three types of orientation-dependent ultrasonic velocities, including Debye average velocities, were evaluated using the calculated SOECs and density of titanium in the same temperature range. Thermophysical properties such as lattice thermal conductivity, thermal relaxation time, thermal energy density, specific heat at constant volume and acoustic coupling constant were evaluated under the same physical conditions. The ultrasonic attenuation due to phonon-phonon interaction is most significant under the chosen physical conditions. The ultrasonic properties of titanium are correlated with thermophysical properties to understand the microstructural features and nature of the material.

PES and transport properties of the He⋯HBr complex from kinetic theory and molecular dynamics simulations.

The ab initio intermolecular potential of the He⋯HBr van der Waals (vdW) complex was calculated at the CCSD(T)/a5zBF level of theory and expanded in terms of the orthogonal Legendre polynomials. The PES then was implemented to calculate the interaction viscosity (η12) and diffusion (D12) coefficients through classical Mason-Monchick approximation (MMA), quantum mechanical close-coupling (CC), and molecular dynamics (MD) simulations. Energy-dependent Senftleben-Beenakker (SB) cross-sections were calculated using rotationally averaged cross-sections, and Boltzmann averaging was used to reveal the temperature dependence of the SB cross-sections over the temperature range of T = 50-1000 K. The calculated transport properties from MMA are in close agreement with the CC results, especially for temperatures lower than T = 900 K. The ab initio potential data then were used to derive LJ (12,6) and Vashishta MD force fields, and the equilibrium MD simulation methods were implemented to extract η12 and D12 coefficients using Einstein formulas. It was found that the Vashishta 3-body interaction potential model shows better accuracy than the LJ (12,6) model in MD simulations of D12. For η12, however, both MD potential models are successful, and an average absolute deviation of lower than 1% was obtained when compared to the quantum mechanical CC method.

Drag on a sphere in a slow flow of a binary mixture of rarefied gases

The drag force on a sphere in an isothermal binary mixture of rarefied gases is calculated on the basis of the McCormack model for the linearized Boltzmann equation. The diffuse scattering of the gas–surface interaction law is assumed as the boundary condition. The rigid-spheres model of interatomic interaction potential is used as well as ab initio potentials for helium, argon, and krypton gases. The force is obtained in a wide range of the gas rarefaction, which covers the free molecular, transition, and slip regimes of the gas flow. In the free molecular and slip flow regimes, the problem is solved analytically, while in the transition regime, the system of kinetic equations is solved numerically via the discrete velocity method optimized to overcome the problem of discontinuity of the distribution function of molecular velocities on the convex surface. The calculations are carried out for the mixtures helium–argon and helium–krypton at 300 K. In the slip flow regime, the data available in the literature for the viscous slip coefficient of the helium–argon mixture are used, while for the mixture helium–krypton, it is calculated. The influence of the interatomic interaction potential, molar fraction, and ratio of atomic mass of species in the mixture on the drag force is analyzed.

Dynamic surface chemistry and interparticle interactions mediating chemically fueled dissipative assembly of colloids

HypothesisDissipative assembly of colloids involves using a chemical fuel to temporarily activate organic colloid surface ligands to an assembly prone state. Colloids assemble into transient aggregates that disintegrate after the fuel is consumed. The underlying colloidal interactions controlling dissipative assembly have not been rigorously identified or quantified. We expect that fuel concentration dependent dissipative assembly behavior can be reconciled with measurements of dynamic colloid surface chemistry and colloidal interactions. ExperimentsCarbodiimide chemistry was utilized to induce dissipative assembly of carboxylic acid functionalized polystyrene colloids. We measured aggregation kinetics, colloid surface hydrophobicity, and zeta potential as a function of time, which established that colloids underwent dissipative assembly for fuel concentrations between 5 and 12.5 mM and irreversible aggregation at higher fuel concentrations due to transient changes in surface chemistry. FindingsWe formulated a pairwise colloidal interaction potential model including hydrophobic interactions quantified by fluorescence binding experiments. Fuel concentrations causing dissipative assembly displayed a transient increase in secondary minimum depth and a primary maximum much larger than the thermal potential. Fuel concentrations leading to irreversible aggregation displayed a primary maximum smaller than the thermal potential. This is the first study to quantify surface chemistry and interparticle interactions during dissipative colloid assembly and represents a foundational step in rationally designing more complex dissipative assembly systems.

Comparative Study of the Adsorption of 1- and 2-Propanol on Ice by Means of Grand Canonical Monte Carlo Simulations

In this paper, we use Grand Canonical Monte Carlo simulations to compare the adsorption characteristics of two propanol isomers (1- and 2-propanol) on crystalline ice, at the temperature of 227 K (i.e., typical of the Earth’s troposphere), for which experimental data are available in the literature. The adsorption isotherms simulated for these two isomers show a very good agreement with the reported experimental data, giving thus confidence in the two interaction potential models used in the calculations. The results of the simulations thus nicely support the experimental conclusion that 2-propanol is preferentially adsorbed on ice with respect to 1-propanol, at least in the low pressure range where only a few molecules are trapped by the ice surface. The accuracy of the approach used, as tested here in tropospheric conditions, opens the way for its use in modeling studies also relevant to astrophysical context.

Analysis of Lane-Changing Decision-Making Behavior and Molecular Interaction Potential Modeling for Connected and Automated Vehicles

With the technical support of an intelligent networking environment, autonomous driving technology is facing a new stage of development, and the decision-making behavior of autonomous vehicles is changing fundamentally, so it is urgent to explore the lane-changing decision-making behavior mechanism of autonomous driving. Firstly, through the analysis of system similarity, the similarity between autonomous vehicles and moving molecules is sought, and the attraction and repulsion between molecules are applied to the lane-changing process of vehicles to effectively recognize the traffic scene of lane-changing vehicles. Secondly, the molecular interaction potential is introduced to unify the attraction and repulsion, and explore the dynamic influencing factors of lane-changing behavior for vehicles. Moreover, we systematically analyze the interaction relationship in the lane-changing process of Connected and Automated Vehicles, and establish the molecular interaction potential lane-changing model to explore the lane-changing decision-making behavior mechanism. Furthermore, we study the impact of micro lane-changing behavior on macro traffic flow. Finally, the SL2015 lane-changing model and the molecular interaction potential lane-changing model are compared and analyzed by using the SUMO platform. The results show that the speed fluctuation of Connected and Automated Vehicles based on the molecular interaction potential lane-changing model is reduced by 15.5%, and the number of passed vehicles is increased by 3.26% on average, which has better safety, stability, and efficiency. The molecular interaction potential modeling of lane-changing decision-making behavior for Connected and Automated Vehicles comprehensively considers the interaction relationship of dynamic factors in the traffic environment, and scientifically shows the lane-changing decision-making mechanism of Connected and Automated Vehicles.

Temperature-Dependent Ultrasonic Properties of Semiconducting M<sub>2</sub>CO<sub>2</sub> (M= Ti, Zr, Hf) MXenes

Here, we have studied the elastic, ultrasonic, mechanical, and thermal behavior of temperature-dependent hexagonal oxygen-functionalized M2CO2 (M= Ti, Zr, Hf) MXenes. The higher-order linear and nonlinear elastic constants, viz., second-order (SOECs), and third-order (TOECs) have been computed using the Lenard Jones interaction potential model. For mechanical characterization, bulk modulus (B), shear modulus (G), Young's modulus (Y), Pugh's ratio (B / G), Poisson's ratio, and anisotropic index are evaluated using SOECs. Born's stability and Pugh's criteria are used to examine the nature and strength of the MXenes in all the temperatures. For the investigation of anisotropic behavior and its thermophysical properties, temperature-dependent ultrasonic velocities and thermal relaxation time have been calculated along with different orientations from the unique axis of the crystal. The ultrasonic attenuation (UA) of a longitudinal and shear wave due to phonon-phonon (p-p) interaction and thermoelastic relaxation mechanism were investigated for these oxygen-functionalized MXenes. Thermal conductivity is a principal contributor to the behavior of UA due to p-p interactions. Our analysis suggests that semiconductor Ti2CO2 MXenes show superior mechanical properties to other oxygen-functionalized MXenes. Computed elastic, ultrasonic, and thermal properties are correlated to evaluate the microstructural behavior of the materials useful for industrial applications.

Adsorption of C2-C5 alcohols on ice: A grand canonical Monte Carlo simulation study.

In this paper, we report grand canonical Monte Carlo simulations performed to characterize the adsorption of four linear alcohol molecules, comprising between two and five carbon atoms (namely, ethanol, n-propanol, n-butanol, and n-pentanol) on crystalline ice in a temperature range typical of the Earth's troposphere. The adsorption details analyzed at 228K show that, at low coverage of the ice surface, the polar head of the adsorbed molecules tends to optimize its hydrogen bonding with the surrounding water, whereas the aliphatic chain lies more or less parallel to the ice surface. With increasing coverage, the lateral interactions between the adsorbed alcohol molecules lead to the reorientation of the aliphatic chains that tend to become perpendicular to the surface; the adsorbed molecules pointing thus their terminal methyl group up to the gas phase. When compared to the experimental data, the simulated and measured isotherms show a very good agreement, although a small temperature shift between simulations and experiments could be inferred from simulations at various temperatures. In addition, this agreement appears to be better for ethanol and n-propanol than for n-butanol and n-pentanol, especially at the highest pressures investigated, pointing to a possible slight underestimation of the lateral interactions between the largest alcohol molecules by the interaction potential model used. Nevertheless, the global accuracy of the approach used, as tested under tropospheric conditions, opens the way for its use in modeling studies also relevant to another (e.g., astrophysical) context.

Bulk viscosity of gaseous argon from molecular dynamics simulations.

The bulk viscosity of dilute argon gas is calculated using molecular dynamics simulations in the temperature range 150-500K and is found to be proportional to density squared in the investigated range of densities 0.001-1 kg m^{-3}. A comparison of the results obtained using Lennard-Jones and Tang-Toennies models of pair interaction potential reveals that the value of the bulk viscosity coefficient is sensitive to the choice of the pair interaction model. The inclusion of the Axilrod-Teller-Muto three-body interaction in the model does not noticeably affect the values of the bulk viscosity in dilute states, contrary to the previously investigated case of dense fluids.

Mechanical and Thermal Properties of Gd-Doped ZnO Nanorods

All the elastic, mechanical and thermal properties of Gd-doped ZnO nanorods (NRs) have studied using interaction potential model. Gd-doped ZnO nanorods are hexagonal wurtzite structure. The characteristic features of elastic characteristics of Gd-doped ZnO NRs imply that this is mechanically stable. For mechanical characterization, bulk modulus (B), shear modulus (G), Young's modulus (Y), Pugh's ratio (B / G), Poisson’s ratio and anisotropic index are evaluated using second order elastic constants. For the investigation of anisotropic behaviour and thermophysical properties, ultrasonic velocities and thermal relaxation time have been also calculated along with different orientations from the unique axis of the crystal. The mechanical properties of the Gd-doped ZnO nanorods are better than at 6% Gd amount due to minimum attenuation. The obtained results are analyzed to explore the characteristic of ZnO nanorods. Computed elastic, ultrasonic and thermal properties are correlated to evaluate the microstructural behaviour of the materials useful for industrial applications

Shannon entropy of resonant scattered state in the e–C60 elastic collision

Resonance is a remarkable feature in elastic scattering and the resonant states of e–C60 scattering are benchmarked using Shannon entropy in the present work. The resonant wavefunction, total cross-section, partial cross-sections, and scattering phase shifts are calculated for the e–C60 scattering to review the localization properties owing to resonance. Three different model interaction potentials are used in the paper to simulate the environment of the C60 shell; annular square well, Gaussian annular square well, and Lorentzian potential. This paper aims to establish a relationship between the Shannon entropy and resonant properties linked with e + C60 scattering. This work introduces the Shannon entropy as an indicator of resonance in elastic scattering and it unveils the susceptibility of entropic properties to the nature of the model potential.

Symmetrical Resonance Mechanism of Elimination of Parasitic Torques of the Permanent Magnets Generator when Starting and Idling

. “Sticking” and vibrations of the stator of permanent magnet generators cause their increased wear, noise; also, their operation efficiency decreases. The article theoretically considers the possibility of eliminating the starting torque and oscillation of the rotation torque of the generator with permanent magnets without load due to mutual compensation of the interaction of coils with the field of permanent magnets at a certain symmetry of this field. The mentioned pheno-menon is called pi-resonance. For the specified class of model interaction potentials of the field of permanent magnets and coils, it has been shown that full compensation occurs with a certain number of coils (Ns) and magnets (Nr), while for other combinations of {Ns, Nr} the interaction is in the nature of oscillations. The corresponding tables for various classes of potentials are given which can serve as a basis for making design decisions when developing generators. Pi-resonance more probably takes place in the case of even number of stator coils and odd number of magnets, as well as with an increase in the number of stator coils. The cases of both one-sided and two-sided arrangement of the stator relative to the rotor are considered. Numerical modelling has shown that the pi-resonance is easily destroyed if the placement of magnets or coils is inaccurate, as well as by the magnet field potential symmetry breaking. An error in the angular arrangement of the coils of 1° can result in the appearance of a significant “cogging” of the rotor with energy of the order of the interaction energy of an isolated magnet – coil pair. A distortion of the symmetry of the potential yields a result similar in scale which is equivalent to the adding of a rump function with the amplitude of 10 % of the amplitude of the symmetric periodic potential. The patterns that have been discovered can be used in the design of efficient generators with reduced level of noise and vibration.

Mechanical, Elastic and Thermal Properties of Hexagonal BC<sub>2</sub>N Superhard Material

The ultrasonic properties of the hexagonal BC2N superhard material were studied at temperature-dependent following the interaction potential model. Higher-order elastic constants are used for the determination of other ultrasonic parameters. The temperature variation of the ultrasonic velocities is evaluated along with different angles with z-axis (unique axis) of the crystal using the second-order elastic constants temperature variation of the thermal relaxation time, and Debye average velocities are also calculated along with the same orientation. The temperature dependency of the acoustic properties is discussed in correlation with elastic, thermal, and mechanical properties. It has been found that thermal conductivity and thermal energy density are the main contributors to the behavior of ultrasonic attenuation as a function of temperature. The responsible cause of attenuation is phonon-phonon interaction. Mechanical properties of BC2N superhard material at temperature 400K are better than at other temperatures because, at this temperature, it has low ultrasonic attenuation. Superhard material BC2N has many industrial and engineering applications.

MPolSys Modeler, a tool for computational modeling of linear polymer systems

The computational study of intermolecular relationships of a given material can be used as a route for predicting quantities impossible or difficult to be determined experimentally. Furthermore properties of new materials can also be predicted by techniques of this type, when they are still in the modeling phase. This technique reproduces the classical dynamic relationships between the constituent elements of the material, atoms or unicorpuscular approximations of molecules, from interaction potential models called force fields. This work aims to develop a tool that performs the composition of linear polymeric chain systems through a self-avoided walk. For this, the concept of self-experimentation of long walks (SAWLC) was used, together with the Python language to develop MpolSys Modeler. This tool is a non-overlapping polymer chain generator, which in turn generates outputs that can be used as input to Moltemplate. To validate the tool's results, experiments were carried out in which the numbers and polymerization chains of the simulated polymer were varied, observing the overlap or not of the molecules that make up the simulation. At the end of the simulations, there were positive results that indicate a promising usage of the tool for the creation of polymers with a high number of chains and degrees of polymerization.