Variation Of Potential Energy Research Articles

Simple and Efficient Equivariant Message-Passing Neural Network Model for Non-local Potential Energy Surfaces.

Machine learning potential has become increasingly successful in atomistic simulations. Many of these potentials are based on an atomistic representation in a local environment, but an efficient description of nonlocal interactions that exceed a common local environment remains a challenge. Herein, we propose a simple and efficient equivariant model, EquiREANN, to effectively represent a nonlocal potential energy surface. It relies on a physically inspired message-passing framework, where the fundamental descriptors are linear combinations of atomic orbitals, while both invariant orbital coefficients and the equivariant orbital functions are iteratively updated. We demonstrate that this EquiREANN model is able to describe the subtle potential energy variation due to the nonlocal structural change with high accuracy and little extra computational cost than an invariant message passing model. Our work offers a generalized approach to create equivariant message-passing adaptations of other advanced local many-body descriptors.

Self-Adaptive Layering Structure of Nanoconfined Fe-Ni Liquids: Origin of the Liquid-Liquid Phase Transition.

Metallic liquids under confinement exhibit different properties compared to those of their corresponding bulk phases, such as miscibility, diffusion, and phase transitions. Unfortunately, the challenges in experimentally characterizing Fe-Ni liquids at the nanoscale and the high cost of first-principles simulations hindered the atom-level understanding that is necessary for controlling Fe-Ni liquids. Here, we report a comprehensive molecular dynamics study of the liquid Fe-Ni alloy confined within nanoslits. Driven by the slit size, the confined Fe-Ni liquid experiences the liquid-liquid phase transition (LLPT) that is characterized by layering transitions. Interestingly, during the LLPT, a transition liquid phase appears, separating two layering phases, which is accompanied by abnormal variations in density, potential energy, and pressure perpendicular to the wall. The Voronoi cluster analysis reveals a self-adaptive local structural evolution in confined Fe-Ni liquids during the LLPT. The effect of temperature, pressure, and composition on the LLPT is investigated. Based on the pressure-confinement phase diagram, the LLPT is mainly induced by confinement under high pressure, while under low pressure, the LLPT is mainly pressure-driven. Our research will stimulate more interest in the phase transition under confinement in a metallic system.

Use of a Refined Theory for Three-Dimensional Bending Analysis of Isotropic Rectangular Thick Plates

In this paper, a refined plate theory (Alternative II theory) is presented for the three-dimensional bending analysis of an Isotropic thick plate. The theory has similarity to the first order shear deformation theory but requires no shear correction factors. The kinematics equations were developed based on the Alternative II Refined plate theory. Thereafter, using a complete three-dimensional constitutive relation, the total potential energy was developed. A governing equation and two compatibility equations were obtained by the variation of the total potential energy with respect to displacement and rotations respectively. Solving the governing and compatibility equations, a polynomial displacement function was obtained. The stiffness coefficients were then obtained using the displacement function. Thereafter, the equations for the in-plane normal and shear stresses, transverse normal and shear stresses as well as the lateral displacement were developed using the stiffness coefficients and the displacement function. Numerical values of the lateral displacement parameters were determined for a rectangular plate of aspect ratio 2.0, 1.0 and 0.5 for span to thickness ratios of 20, 10 and 7.14286. Also, numerical values of the lateral displacement and stresses were determined for a square plate for span to thickness ratios of 4, 10, 100 and 1000. The results from this work were compared with the work of previous researchers using simple percentage difference. It was observed that refined plate theories overestimate the lateral displacement of a plate. Hence, three-dimensional analysis is recommended for thick plate analysis.

SO3NH3 crystal growth in (CH3)3SBr solution

SO3NH3 (Sulfamic acid, or SA) is known for its excellent piezoelectric and optical properties, making it valuable for various optical applications. However, it usually takes weeks to months to grow the SA single crystals with centimeter-scale size by traditional growth method from solution. In this study, we use (CH3)3SBr (Me3SBr) as an additive to enhance the growth rate of SA single crystals, and the growth time was reduced to just 48 h. The mechanism of accelerated crystallization process is attributed to the variations of electrostatic potential and binding energy on SA crystal modified by the additive. In addition, structural analysis and basic characterization on the newly grown SA are performed, and first-principles calculations provide insights into the energy band structure and phonon spectrum.

Study on Coalescence Characteristics and Mechanisms of Salt-laden Droplets Under Electric-magnetic Coupling Field

Abstract Electric-magnetic coupling dehydration technology is a novel method that can significantly improve the efficiency of water-oil separation in water-in-oil (W/O) emulsions. However, the electric-magnetic coupling mechanisms and its influence on droplet coalescence have not been understood from a microscopic perspective, which has become a bottleneck restricting the progress of this technology. In this study, the high-speed microscopic experiment and molecular dynamics (MD) simulation were combined to study the kinetic properties of droplets coalescence under an electric-magnetic coupling field, and the potential mechanisms of electric-magnetic coupling field strengthening droplet coalescence were articulated from the perspective of salt ions migration and energy evolution. The results show that the experiment and simulation have excellent qualitative consistency. As water molecules polarise and migrate, the contact interface between adjacent droplets forms a cone tip during the approach process. The contact point of the droplet forms hydrogen bonds due to the mutual attraction of water molecules, which are then transformed into a continuously expanding liquid bridge. The salt ions in the droplet undergo migration deflection by the electric-magnetic coupling effect, which may affect the surface charge distribution of the droplets. During the process of droplet coalescence, strong electrostatic attraction occurs between molecules, leading to a significant increase in coulomb potential and dominating the overall potential energy variation. However, excessively small molecular spacing induces exchange repulsion, thereby reducing the van der Waals potential. The study results are of guiding significance for sounding droplet dynamics theory and guiding the research and development of electric-magnetic dehydration equipment.

Comparing Earthquake Cycles on Normal and Reverse Faults Based on Simulations With a Dynamic Elasto‐Plastic Model

AbstractShear stress levels on reverse faults are anticipated to be several times higher than on normal faults with the same pore pressure ratio. In addition, ruptures on normal faults release gravitational potential energy, whereas earthquakes on reverse faults expend work in uplifting rocks. In this study, I investigate the significance of these differences for earthquake cycles and I question whether the source of energy driving earthquakes is the same on reverse and normal faults. Based on the assumption that normal and reverse faults have the same background frictional properties and pore pressure states, I use numerical simulations with a two‐dimensional dynamic elastic‐plastic model to show that due to stress differences, earthquakes on reverse faults tend to occur less frequently, produce more coseismic slip and stress drop and involve higher slip rates than ruptures on normal faults with equivalent dimensions. The analysis also shows differences in the energy changes associated with earthquake cycles on reverse and normal faults. However, the earthquakes on both fault types result from abrupt release of elastic strain energy, which proceed and essentially drive variations in gravitational potential energy. Thus, ruptures on both normal and reverse faults are consistent with elastic rebound theory.

Simulation Analysis of a Passive Biped Robot

To more accurately understand the fundamental characteristics of the motion of a passive biped robot and to enhance the guidance provided by model research for the design of practical prototypes, we analyze the characteristics of this passive model and establish the corresponding dynamic model using the Lagrange method. Based on the characteristic that the stable walking cycle gait of the robot manifests as a limit cycle in the phase plane, we study the passive biped model with knee joints through co-simulation using Adams and Matlab. The process of simulating steady-state walking of the ideal model is demonstrated in detail, including the initial conditions required for the robot to achieve periodic steady-state walking, the motion characteristics, and the distribution, variation, and interconversion of kinetic and potential energy during the motion.

Self-propelled directed transport of C60 fullerene on the surface of the cone-shaped carbon nanotubes

Directed transportation of materials at molecular scale is important due to its crucial role in the development of nanoelectromechanical devices, particularly the directional movements along the carbon nanotubes (CNTs), due to the applications of CNTs as nano-manipulators, confined reactors, and drug or other materials delivery systems. In the present investigation, we evaluate the movements of C60 fullerenes on the surface of the cone-shaped CNTs. The fullerene molecules indicate directed motion toward the narrower end of CNTs, which is due to the potential energy gradient along the nanotube length. A continuum model is proposed to evaluate the mechanism of the directed motion and the results of the theoretical model are compared with numerical simulations. Directed movements have been examined at various opening angles of CNTs, considering the trajectories of motions, variation of potential energy, and diffusion coefficients. At smaller opening angles, the driving force on the C60 increases and the molecule experiences more directed transport along the nanotube. The motion of fullerene has also been simulated inside the cone-shaped CNTs, with similar opening angle, and different average radius. At lower average radius of the cone-like nanotubes, the motion of C60 is comparatively more rectilinear. Directional transport of fullerene has been observed in the opposite direction, when the molecule moves on the external surface of the cone-like CNTs, which is due to the stronger interaction of C60 with the parts of the external surface with larger radius. The effect of temperature has been evaluated by performing the simulations at the temperature range of 100 to 400 K. The direction of the velocity reveals that the thermal fluctuations at higher temperatures hinder the directed motion of molecule along the cone-shaped CNTs. The results of the present study propose a new method to obtain directed transport of molecules which can be helpful in different applications such as drug delivery systems.

A numerical model for solitary wave breaking based on the phase-field lattice Boltzmann method

This study presents a numerical investigation of a solitary wave breaking over a slope by using the phase-field lattice Boltzmann method. The incompressible two-phase flow equations are solved by using a velocity-based formulation of the two-phase lattice Boltzmann method with a central-moment collision model to accurately simulate wave breaking problems. For interface capture, a phase-field lattice Boltzmann method that ensures mass conservation is employed. The validity of the proposed method is confirmed through solitary wave propagation and transformation problems, and the obtained results are in good agreement with the experimental and calculated results. The proposed method is then employed to analyze wave breaking on a slope, demonstrating strong concordance with experimental data and existing computational findings. By analyzing the instantaneous flow characteristics and the temporal evolution of the variation in kinetic, potential, and total energy from deep to shallow water, the model can reveal the macroscopic characteristics of solitary wave breaking. Because the phase-field model effectively simulates wave breaking and air entrainment, it can depict wave energy dissipation more accurately than the single-phase lattice Boltzmann method with free surface tracking.

Improved Precipitation Diurnal Cycle in GFDL Climate Models With Non‐Equilibrium Convection

AbstractMost global climate models with convective parameterization have trouble in simulating the observed diurnal cycle of convection. Maximum precipitation usually happens too early during summertime, especially over land. Observational analyses indicate that deep convection over land cannot keep pace with rapid variations in convective available potential energy, which is largely controlled by boundary‐layer forcing. In this study, a new convective closure in which shallow and deep convection interact strongly, out of equilibrium, is implemented in atmosphere‐only and ocean‐atmosphere coupled models. The diurnal cycles of convection in both simulations are significantly improved with small changes to their mean states. The new closure shifts maximum precipitation over land later by about three hours. Compared to satellite observations, the diurnal phase biases are reduced by half. Shallow convection to some extent equilibrates rapid changes in the boundary layer at subdiurnal time scales. Relaxed quasi‐equilibrium for convective available potential energy holds in significant measure as a result. Future model improvement will focus on the remaining biases in the diurnal cycle, which may be further reduced by including stochastic entrainment and cold pools.

An innovative deformation coordination method for analyzing distortion effects on box girders

A deformation coordination method is proposed in this study to account for the distortion effects on a box girder. The differential equation for distortion in vertical web box girders is derived based on the deformation coordination condition of the distortion angle, considering both external loads and internal forces. Subsequently, a comparative analysis is conducted to explore the similarities and differences between the differential equations derived from the proposed deformation coordination method, the plate element analysis method and the total potential energy variation method. The accuracy of the proposed approach is verified through bench-scale tests and numerical simulations. The findings indicate that the derived governing distortion differential equation and distortion attenuation coefficients in the proposed method align with those obtained from the plate element analysis method and the total potential energy variational method, which enhances the applicability to allow for the distortion equations to be obtained simply by calculating the distortion displacements. The analytical findings regarding the distortion warping normal stresses on the cross-sections of the box girders demonstrate favorable correspondence with the experimental results, displaying an acceptable error ranging from − 0.3% to 5.4%. Moreover, the peak of distortion warping normal stresses on the mid-span cross-section increases with higher span-to-depth ratios and height-to-thickness ratios of the web. Consequently, augmenting the thickness of the box wall proves to be an effective means of reducing the distortion effect in box girders.

Alternative II Theory Solution for a Thick Rectangular Anisotropic Plate Under in-Plane and Lateral Loads

This work investigated the application of the Alternative II refined plate theory in the analysis of an anisotropic plate subjected to in-plane and lateral loads. The kinematic equations developed from the Alternative II Refined plate theory were used together with a complete three-dimensional constitutive relation to obtain the total potential energy of an anisotropic plate under lateral and in-plane loads. General variation of the total potential energy was done, a governing equation and two compatibility equations were obtained. A polynomial displacement function was obtained by solving the governing and compatibility equations. This was used to obtain peculiar displacement functions by satisfying the boundary conditions of any plate. The stiffness coefficients were obtained using the displacement function. With the displacement functions and the stiffness coefficients, the equations for the in-plane normal and shear stresses as well as the transverse normal and shear stresses were determined for any applied lateral load when the applied in-plane load is a fraction of the buckling load. Also, the equations for the displacements of the plate were determined. Numerical values of the stresses and displacement parameters were determined for span to thickness ratios of 5, 10, 20 and 100 at angle of fiber orientations of 0 and aspect ratios of 1, 1.5 and 2.0 when the ratio of applied in-plane load to buckling load are 0, 0.25 and 0.5. Using simple percentage difference, the results from this work were compared with the works of previous researchers.

Electrochemical measurement of the electronic structure of graphene via quantum mechanical rate spectroscopy

Quantum-rate theory defines a quantum mechanical rate ν that complies with the Planck–Einstein relationship E=hν, where ν=e2/hCq is a frequency associated with the quantum capacitance Cq, and E=e2/Cq is the energy associated with ν. Previously, this definition of ν was successfully employed to define a quantum mechanical meaning for the electron-transfer (ET) rate constant of redox reactions, wherein faradaic electric currents involved with ET reactions were demonstrated to be governed by relativistic quantum electrodynamics at room temperature (Bueno, 2023c).This study demonstrated that the definition of ν entails the relativistic quantum electrodynamics phenomena intrinsically related to the perturbation of the density-of-states dn/dE=Cq/e2 by an external harmonic oscillatory potential energy variation. On this basis, the electronic structure of graphene embedded in an electrolyte environment was computed. The electronic structure measured using quantum-rate spectroscopy (QRS) is in good agreement with that measured through angle-resolved photo-emission spectroscopy (ARPES) or calculated via computational density-functional theory (DFT) methods.Electrochemical QRS has evident experimental advantages over ARPES. For instance, QRS enables obtaining the electronic structure of graphene at room temperature and in an electrolyte environment, whereas ARPES requires low temperature and ultrahigh-vacuum conditions. Furthermore, QRS can operate in-situ using a hand-held, inexpensive piece of equipment, whereas ARPES necessarily requires expensive and cumbersome apparatus.

Effect of cooling rate on solidification points and atomic structures of metal nanoclusters: a molecular dynamics simulation study

In this work, the micro-structural evolution during the solidification process of three metal nanoclusters (copper, nickel, and silver) containing 2048 atoms each, subjected to different cooling rates are investigated. Molecular dynamics (MD) simulations in conjunction with modified embedded atom method (MEAM) potentials have been employed to carry out the work. For different cooling rates, the solidification points of the nanoclusters are estimated from the variation in average potential energy of the systems during the crystallization process, and the structural evolutions are analysed by utilising radial distribution function and common neighbour analysis method. The results advocate that the cooling rate has a profound impact on the structures of the solidified nanoclusters. The critical cooling rate for each nanocluster has been captured, where a glassy/amorphous structure is observed. Polycrystalline nano-structures (consisting of amorphous, FCC and HCP) are observed below these critical cooling rates and the number of close-packed structures (FCC, HCP) are found to decrease with the increase in cooling rate. The findings of this work would be helpful in various practical applications of the metal nanoclusters, where the structure of nanoclusters directly affect.

Effect of sintering process on mechanical properties of uniaxial tensile sintered nano-silver component

In the paper, the mechanical properties of uniaxial tensile sintered nano-silver components were investigated by molecular dynamics method, and the effects of sintering pressure and temperature on them were analyzed. The sintered body was obtained by sintering three adjacent cubes, and the sintered nano-silver component under uniaxial tension was cut from the existing sintered body. The results show that the potential energy decreases while the kinetic energy has a jump. The higher the sintering pressure, the earlier the nano-silver sintering begins. Temperature has little effect on sintering time. When sintered nano-silver components are uniaxial tensile, the greater the sintering pressure, the greater the rising absolute value of the potential energy, and the greater the yield stress. When the sintering temperature is 250°C, the variation of potential energy is large and the yield stress is high. The paper aims to supplement and guide the mechanical properties of sintered nano-silver.

Regular double-helix self-assembled from two poly(p_phenylene) chains under the inducement of metal nanoclusters

Molecular dynamics simulations demonstrate that metal nanoclusters (NCs) can induce two poly(p_phenylene) (PP) chains to self-assemble into regular double-helix through noncovalent interactions. In the process, the van der Waals (vdW) energy dominates the helically self-assembly of PP chains. The corresponding mechanism is revealed from the evolution of atomic conformations and the variation of total potential energy including its energy components. When adsorption energy of PP and NCs between 1.32 and 12.87 kcal/mol·Å, NCs can induce the helical self-assembly of two PP chains to form regular double-helix. The NC diameter and relative position of PP and NCs have a great influence on the formation of the double helix. Furthermore, the PP chain interacting with different number of Ni NCs are also studied.

Stability to the finite disturbance of the critical equilibrium for three struts

In this paper, sufficient conditions of stability for the critical equilibrium of Euler struts with three typical rigid boundaries, that is, one end fixed and the other clamped in rotation, fixed-free, pinned-pinned, are studied. A construction of a double orthonormal Fourier series for angle is presented for the three struts, respectively. By the double orthonormal series, the second variation of potential energy can be expressed in a diagonal quadratic form. The second variation of potential energy is proved to be semi-positive-definite. Sum of higher order variations than the second-order variation of potential energy is identically positive. The critical equilibrium is stable to disturbance with finite value, which is called “stable in the large” in the sense of Lagrange-Dirichlet stability criterion. Stability to disturbance with finite value includes the stability to disturbance with infinitesimal value in Koiter’s theory. In addition, there is a constraint on the angle for the pinned-pinned strut, which is not included in Koiter’s theory.

On the influence of edge damage on thermally induced buckling of stepped circular bi-laminates

The influence of edge damage on thermo-mechanical buckling of stepped circular bi-laminates is examined analytically. The nonlinear equations of equilibrium, the associated boundary conditions and the transversality conditions for the propagating interior boundaries of a region of sliding contact are derived via the Principal of Stationary Potential Energy as a propagating boundary problem in the calculus of variations. The problem is ultimately recast in a mixed formulation expressed in terms of the membrane forces and the transverse displacements of the composite structure. A loading parameter is identified and closed form analytical solutions to the resulting non-linear problem are determined. In addition, a stability criterion is established based on the second variation of the total potential energy of the structure, and qualitative behavior concerning contact is deduced analytically. Results of numerical simulations based on the analytical solutions established herein are generated and the phenomenon of “sling-shot buckling” is observed, whereby the structure first deflects in one direction upon heating (or cooling) and then, when a critical temperature is achieved, dynamically “sling-shots” from the current equilibrium configuration to an alternate equilibrium configuration possessing deflections in the opposite sense. In addition, the phenomenon of “buckle-trapping” is observed for stepped circular bi-laminates with hinged-fixed supports, as well as for clamped-fixed structures with relatively large damaged area. A robust mixture of contact behavior, including propagating sliding contact, edge contact and no contact, and the transition from one form of contact to another, is exhibited for both pre-buckling and post-buckling configurations. The influence of edge damage on critical load and characteristic behavior is assessed.

Self-assembly and tiling of a prochiral hydrogen-bonded network: bi-isonicotinic acid on coinage metal surfaces

Submolecular resolution scanning tunnelling microscopy and qPlus atomic force microscopy reveal that, close to thermal equilibrium, bi-isonicotinic acid (4,4'-COOH-2,2'-bpy) assembles into extended molecular rows on both Au(111) and Ag(100) surfaces, driven primarily by the formation of OH··· N hydrogen bonds. Both the intermolecular separation and inter-row spacing for Au(111) and Ag(100) are identical within experimental uncertainty, highlighting that the assembly of bi-isonicotinic acid networks on both metal surfaces is predominantly driven by intermolecular hydrogen-bonding and that the potential energy variation due to the substrate has relatively little influence. Nonetheless, the surface plays a key role in molecular organisation: symmetry-breaking induces prochiral behaviour, which drives the molecular enantiomers to form a racemic mixture of rows of different handedness. We adapt a tiling model previously introduced to model the formation of 2D networks of tetracarboxylic derivatives [Blunt et al. Science 322, 1077 (2008)] to the bi-isonicotinic acid system, providing key insights into the growth kinetics and attaining good agreement with the molecular morphologies observed in experiment.

Assessment of CO2-Oil swelling behavior using molecular dynamics simulation: CO2 utilization and storage implication

CO2 injection into petroleum reservoirs is an effective enhanced oil recovery (EOR) method that can increase the recovery of oil while reducing CO2 emissions into the atmosphere. To ensure successful implementation of CO2 EOR, a detailed understanding of reservoir fluid properties and the phase behavior of CO2-oil mixtures at different scales is required. The extent to which CO2 injection improves the oil recovery factor is heavily dependent on the swelling behavior of CO2-oil mixtures, which can be quantified by swelling factors. In this study, we model a CO2-oil swelling test using molecular dynamics (MD) simulations to calculate the swelling factors over a pressure range of 24.8 to 68 bar at a temperature of 303.15 K for an actual crude oil sample. The multicomponent molecular model of the oil is built using 1000 molecules of six hydrocarbons, based on the compositional analysis of the oil sample. CO2 molecules are then added to the system at several pressure steps, based on experimental CO2 solubility data, and the resulting swelling factors are compared to their corresponding experimental values. The results of this study demonstrate that the MD simulation model can be successfully used to investigate CO2-oil swelling behavior and accurately predict the swelling factors with a minor mean percentage error of 6%. Additionally, analysis of potential energy variations due to interactions between different molecules in the system under increasing pressures and CO2 mole fractions indicates that the swelling process is primarily controlled by changes in intermolecular forces between CO2-oil and oil-oil molecular pairs, while the effect of CO2-CO2 molecular potentials on oil swelling is minimal. This work highlights the ability of the MD simulation technique to model the complex phase behavior of CO2-oil mixtures and provides unique insights into the molecular-scale mechanisms of CO2 dissolution in oil and the resulting swelling phenomenon.