Short-range Repulsive Interactions Research Articles

Study of structural phase transition and elastic properties of ZnTe semiconducting compound under high pressure

The high-pressure structural phase transition and pressure induced elastic properties of cubic zinc-blende phase (B3) to rock-salt phase (B1) structure of Zinc Telluride (ZnTe) semiconducting compound were studied by using the effective inter-ionic potential method, which contains the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach. The structural phase transition from B3 to B1 structure is reflected using estimated values of phase transition pressure and volumetric abrupt changes in the pressure–volume phase diagram. The calculated results first predict the phase transformation of ZnTe from B3 to B1, which occurs at 19GPa and is consistent with the reported data. Later on, using the effective inter-ionic potential technique, we were able to predict the second order elastic characteristics of the ZnTe system.

Machine-learning interatomic potential for radiation damage effects in bcc-iron

We introduce a machine-learning interatomic potential for bcc iron based on the moment tensor potential framework and a hybridization scheme of distinct sub-potentials. With an orientation on radiation damage effects, the potential shows good transferability from properties relevant to collision cascade to those relevant to plasticity. Specifically, the potential accurately reproduces the short-range repulsive interactions, the generalized stacking fault energies, the dislocation core structures and the formation energies of defect clusters. The general purposed applicability of the potential enables simulation of radiation damage effects in bcc iron with an accurate and an unprecedentedly unified theoretical model.

Structural and Dynamical Behaviour of Colloids with Competing Interactions Confined in Slit Pores.

Systems with short-range attractive and long-range repulsive interactions can form periodic modulated phases at low temperatures, such as cluster-crystal, hexagonal, lamellar and bicontinuous gyroid phases. These periodic microphases should be stable regardless of the physical origin of the interactions. However, they have not yet been experimentally observed in colloidal systems, where, in principle, the interactions can be tuned by modifying the colloidal solution. Our goal is to investigate whether the formation of some of these periodic microphases can be promoted by confinement in narrow slit pores. By performing simulations of a simple model with competing interactions, we find that both the cluster-crystal and lamellar phases can be stable up to higher temperatures than in the bulk system, whereas the hexagonal phase is destabilised at temperatures somewhat lower than in bulk. Besides, we observed that the internal ordering of the lamellar phase can be modified by changing the pore width. Interestingly, for sufficiently wide pores to host three lamellae, there is a range of temperatures for which the two lamellae close to the walls are internally ordered, whereas the one at the centre of the pore remains internally disordered. We also find that particle diffusion under confinement exhibits a complex dependence with the pore width and with the density, obtaining larger and smaller values of the diffusion coefficient than in the corresponding bulk system.

Machine-learning interatomic potential for W–Mo alloys

In this work, we develop a machine-learning interatomic potential for W x Mo1−x random alloys. The potential is trained using the Gaussian approximation potential framework and density functional theory data produced by the Vienna ab initio simulation package. The potential focuses on properties such as elastic properties, melting, and point defects for the whole range of W x Mo1−x compositions. Moreover, we use all-electron density functional theory data to fit an adjusted Ziegler–Biersack–Littmarck potential for the short-range repulsive interaction. We use the potential to investigate the effect of alloying on the threshold displacement energies and find a significant dependence on the local chemical environment and element of the primary recoiling atom.

Modification of short-range repulsive interactions in ReaxFF reactive force field for Fe–Ni–Al alloy* *Project supported by the National Magnetic Confinement Fusion Energy Research Project (Grant Nos. 2019YFE03120003, 2018YFE0307100, and 2017YFE0302500) and the National Natural Science Foundation of China (Grant Nos. 11975034, 11921006, 12004010, and U20B2025).

The short-range repulsive interactions of any force field must be modified to be applicable for high energy atomic collisions because of extremely far from equilibrium state when used in molecular dynamics (MD) simulations. In this work, the short-range repulsive interaction of a reactive force field (ReaxFF), describing Fe–Ni–Al alloy system, is well modified by adding a tabulated function form based on Ziegler–Biersack–Littmark (ZBL) potential. The modified interaction covers three ranges, including short range, smooth range, and primordial range. The short range is totally predominated by ZBL potential. The primordial range means the interactions in this range is the as-is ReaxFF with no changes. The smooth range links the short-range ZBL and primordial-range ReaxFF potentials with a taper function. Both energies and forces are guaranteed to be continuous, and qualified to the consistent requirement in LAMMPS. This modified force field is applicable for simulations of energetic particle bombardments and reproducing point defects' booming and recombination effectively.

Repulsive properties of hadrons in lattice QCD data and neutron stars

Second-order susceptibilities $\chi^{11}_{ij}$ of baryon, electric, and strangeness, $B$, $Q$, and $S$, charges, are calculated in the Chiral Mean Field (CMF) model and compared to available lattice QCD data. The susceptibilities are sensitive to the short range repulsive interactions between different hadron species, especially to the hardcore repulsion of hyperons. Decreasing the hyperons size, as compared to the size of the non-strange baryons, does improve significantly the agreement of the CMF model results with the Lattice QCD data. The electric charge-dependent susceptibilities are sensitive to the short range repulsive volume of mesons. The comparison with lattice QCD data suggests that strange baryons, non-strange mesons and strange mesons have significantly smaller excluded volumes than non-strange baryons. The CMF model with these modified hadron volumes allows for a mainly hadronic description of the QCD susceptibilities significantly above the chiral pseudo-critical temperature. This improved CMF model which is based on the lattice QCD data, has been used to study the properties of both cold QCD matter and neutron star matter. The phase structure in both cases is essentially unchanged, i.e. a chiral first-order phase transition occurs at low temperatures ($T_{\rm CP}\approx 17$ MeV), and hyperons survive deconfinement to higher densities than non-strange hadrons. The neutron star maximal mass remains close to 2.1$M_\odot$ and the mass-radius diagram is only modified slightly due to the appearance of hyperons and is in agreement with astrophysical observations.

Novel soliton in dipolar BEC caused by the quantum fluctuations

Solitons in the extended hydrodynamic model of the dipolar Bose-Einstein condensate with quantum fluctuations are considered. This model includes the continuity equation for the scalar field of concentration, the Euler equation for the vector field of velocity, the pressure evolution equation for the second rank tensor of pressure, and the evolution equation for the third rank tensor. Large amplitude soliton solution caused by the dipolar part of quantum fluctuations is found. It appears as the bright soliton. Hence, it is the area of compression of the number of particles. Moreover, it exists for the repulsive short-range interaction.

Interacting hadron resonance gas model in magnetic field and the fluctuations of conserved charges

In this paper we discuss the interacting hadron resonance gas (HRG) model in presence of a constant external magnetic field. The short range repulsive interaction between hadrons are accounted through Van der Waals excluded volume correction to the ideal gas pressure. Here we take the sizes of hadrons as r π (pion radius) = 0 fm, r K (kaon radius) = 0.35 fm, r m (all other meson radii) = 0.3 fm and r b (baryon radii) = 0.5 fm. We analyse the effect of uniform background magnetic field on the thermodynamic properties of interacting hadron gas. We especially discuss the effect of interactions on the behaviour of magnetization of low temperature hadronic matter. The vacuum terms have been regularized using magnetic field independent regularization scheme. We find that the magnetization of hadronic matter is positive which implies that the low temperature hadronic matter is paramagnetic. We further find that the repulsive interactions have very negligible effect on the overall magnetization of the hadronic matter and the paramagnetic property of the hadronic phase remains unchanged. We have also investigated the effects of short range repulsive interactions as well as the magnetic field on the baryon and electric charge number susceptibilities of hadronic matter within the ambit of excluded volume HRG model.

Cucker–Smale Type Dynamics of Infinitely Many Individuals with Repulsive Forces

We study the existence and uniqueness of the time evolution of a system of infinitely many individuals, moving in a tunnel and subjected to a Cucker-Smale type alignment dynamics with compactly supported communication kernels and to short-range repulsive interactions to avoid collisions.

Linear and nonlinear rheology of oil in liquid crystal emulsions

While the majority of experimental and numerical studies focus on yield stress fluids with short-range repulsive interactions, the effect of long-range interaction is rarely known. In this work, we studied the linear and nonlinear rheological behavior of a model oil in nematic liquid crystal emulsions, which exhibit long-range droplet-droplet interaction. The characteristic of long-range interaction, attractive at large droplet separation and repulsive at a small surface distance, was inferred from the morphology and thixotropy of emulsions. We suggested a model accounting for the plateau modulus purely due to the long-range repulsive interaction. We further illustrated that neither the yield stress nor the relaxation time followed a simple power-law scaling with respect to the distance to jamming. The rescaled steady and dynamic flow curves could not collapse on master curves above jamming transition when the long-range and short-range repulsive interactions contribute simultaneously.

Structure and stability of vacancy–solute complexes in Al–Mg–Si alloys

This study investigates the structure and stability of vacancy–solute complexes in Al–Mg–Si alloys using first-principles calculations along with the prediction of initial structures using multiple linear regression analysis. In Al–Mg and Al–Si binary alloys, vacancy–solute complexes become unstable when more than five solute atoms are combined with a vacancy, due to the repulsive interactions between adjacent atom pairs. In Al–Mg–Si alloys, the formation energy of the vacancy–solute complexes continues to decrease as the number of solute atoms increase. The stability of vacancy–solute complexes mainly arises from the Mg–Si bonds formed with the increasing number of solute atoms. The combination of inward displacement of the Mg atoms and outward displacement of the Si atoms accommodates the increase in the number of Mg–Si bonds. Owing to short range repulsive interatomic interactions, Mg–Mg bonds cannot be formed in vacancy–solute complexes of Al–Mg–Si alloys. However, Si–Si bonds are a preferable alternative to enhance stability in vacancy–solute complexes, despite their decreased strength compared with Mg–Si, Al–Mg, and Al–Si bonds. The concentration of Si atoms in the vacancy–solute complexes is always larger than that of Mg atoms at finite temperatures. The stability of the Si-rich composition originates from the difference between the Si–Si and Mg–Mg interactions in the vacancy–solute complexes.

Improved Alchemical Free Energy Calculations with Optimized Smoothstep Softcore Potentials.

Progress in the development of GPU-accelerated free energy simulation software has enabled practical applications on complex biological systems and fueled efforts to develop more accurate and robust predictive methods. In particular, this work re-examines concerted (a.k.a., one-step or unified) alchemical transformations commonly used in the prediction of hydration and relative binding free energies (RBFEs). We first classify several known challenges in these calculations into three categories: endpoint catastrophes, particle collapse, and large gradient-jumps. While endpoint catastrophes have long been addressed using softcore potentials, the remaining two problems occur much more sporadically and can result in either numerical instability (i.e., complete failure of a simulation) or inconsistent estimation (i.e., stochastic convergence to an incorrect result). The particle collapse problem stems from an imbalance in short-range electrostatic and repulsive interactions and can, in principle, be solved by appropriately balancing the respective softcore parameters. However, the large gradient-jump problem itself arises from the sensitivity of the free energy to large values of the softcore parameters, as might be used in trying to solve the particle collapse issue. Often, no satisfactory compromise exists with the existing softcore potential form. As a framework for solving these problems, we developed a new family of smoothstep softcore (SSC) potentials motivated by an analysis of the derivatives along the alchemical path. The smoothstep polynomials generalize the monomial functions that are used in most implementations and provide an additional path-dependent smoothing parameter. The effectiveness of this approach is demonstrated on simple yet pathological cases that illustrate the three problems outlined. With appropriate parameter selection, we find that a second-order SSC(2) potential does at least as well as the conventional approach and provides vast improvement in terms of consistency across all cases. Last, we compare the concerted SSC(2) approach against the gold-standard stepwise (a.k.a., decoupled or multistep) scheme over a large set of RBFE calculations as might be encountered in drug discovery.

Probing the interactions between interstitial hydrogen atoms in niobium through density functional theory calculations

Past experiments about hydrogen absorption in niobium have revealed specific properties about interactions between interstitial hydrogen atoms. It has been reported that there are long-range attractive and short-range repulsive interactions between interstitial hydrogen atoms in niobium. It has also been reported that these interactions are of many-body nature. While previous understanding of these interactions is based on experimental inferences from past experiments, through these calculations, for the first time, we can understand the nature of the interactions at a fundamental level. In this work, we use density functional theory calculations to study the interactions of interstitial hydrogen atoms in niobium. We report here that these interactions are a combination of an attractive, indirect image interaction and a repulsive, direct interaction. Through our calculations, we also infer here that these interactions indeed have many-body characteristics.

Self-templating assembly of soft microparticles into complex tessellations.

Encoding Archimedean and non-regular tessellations in self-assembled colloidal crystals promises unprecedented structure-dependent properties for applications ranging from low-friction coatings to optoelectronic metamaterials1-7. Yet, despite numerous computational studies predicting exotic structures even from simple interparticle interactions8-12, the realization of complex non-hexagonal crystals remains experimentally challenging13-18. Here we show that two hexagonally packed monolayers of identical spherical soft microparticles adsorbed at a liquid-liquid interface can assemble into a vast array of two-dimensional micropatterns, provided that they are immobilized onto a solid substrate one after the other. The first monolayer retains its lowest-energy hexagonal structure and acts as a template onto which the particles of the second monolayer are forced to rearrange. The frustration between the two lattices elicits symmetries that would not otherwise emerge if all the particles were assembled in a single step. Simply by varying the packing fraction of the two monolayers, we obtain not only low-coordinated structures such as rectangular and honeycomb lattices, but also rhomboidal, hexagonal and herringbone superlattices encoding non-regular tessellations. This is achieved without directional bonding, and the structures formed are equilibrium structures: molecular dynamics simulations show that these structures are thermodynamically stable and develop from short-range repulsive interactions, making them easy to predict, and thus suggesting avenues towards the rational design of complex micropatterns.

Oscillatory behavior in a system of swarmalators with a short-range repulsive interaction.

One of the computational models proposed to study emerging phenomena in decentralized systems is the swarmalator model [Nat. Commun. 8, 1504 (2017)2041-172310.1038/s41467-017-01190-3], where only long-range interactions are considered. But in living systems many of the collective behaviors observed arise from the combined effect of long- and short-range interactions. In this work we present an extension to the swarmalator model which includes a Gaussian short-range repulsive term of the type 1/σe^{-|x|^{2}/σ} along with the results of numerical simulations. Using several order parameters we can distinguish between static and dynamic aggregations and between synchronous and asynchronous states. We have found six long-term collective states, some of them not previously reported and the most remarkable one showing oscillatory collective behavior. The results obtained show a multiplicity of complex behaviors that extend the applicability of the swarmalator model.

Accessing the gluonic structure of light nuclei at a future electron-ion collider

We show how exclusive vector meson production off light ions can be used to probe the spatial distribution of small-$x$ gluons in the deuteron and $^3$He wave functions. In particular, we demonstrate how short range repulsive nucleon-nucleon interactions affect the predicted coherent $J/\Psi$ production spectra. Fluctuations of the nucleon substructure are shown to have a significant effect on the incoherent cross section above $|t|\gtrsim 0.2\,\mathrm{GeV}^2$. By explicitly performing the JIMWLK evolution, we predict the $x$-dependence of coherent and incoherent cross sections in the EIC energy range. Besides the increase of the average size of the nucleus with decreasing $x$, both the growth of the nucleons and subnucleonic hot spots are visible in the cross sections. The decreasing length scale of color charge fluctuations with decreasing $x$ is also present, but may not be observable for $|t|<1\,\mathrm{GeV}^2$, if subnucleonic spatial fluctuations are present.

Hyperuniform vortex patterns at the surface of type-II superconductors

A many-particle system must posses long-range interactions in order to be hyperuniform at thermal equilibrium. Hydrodynamic arguments and numerical simulations show, nevertheless, that a three-dimensional elastic-line array with short-ranged repulsive interactions, such as vortex matter in a type-II superconductor, forms at equilibrium a class-II hyperuniform two-dimensional point pattern for any constant-$z$ cross section. In this case, density fluctuations vanish isotropically as $\sim q^{\alpha}$ at small wave-vectors $q$, with $\alpha=1$. This prediction includes the solid and liquid vortex phases in the ideal clean case, and the liquid in presence of weak uncorrelated disorder. We also show that the three-dimensional Bragg glass phase is marginally hyperuniform, while the Bose glass and the liquid phase with correlated disorder are expected to be non-hyperuniform at equilibrium. Furthermore, we compare these predictions with experimental results on the large-wavelength vortex density fluctuations of magnetically decorated vortex structures nucleated in pristine, electron-irradiated and heavy-ion irradiated superconducting BiSCCO samples in the mixed state. For most cases we find hyperuniform two-dimensional point patterns at the superconductor surface with an effective exponent $\alpha_{\text{eff}} \approx 1$. We interpret these results in terms of a large-scale memory of the high-temperature line-liquid phase retained in the glassy dynamics when field-cooling the vortex structures into the solid phase. We also discuss the crossovers expected from the dispersivity of the elastic constants at intermediate length-scales, and the lack of hyperuniformity in the $x\,-y$ plane for lengths $q^{-1}$ larger than the sample thickness due to finite-size effects in the $z$-direction.

Coupled superfluidity of binary Bose mixtures in two dimensions

We consider a two-component Bose gas in two dimensions at low temperature with short-range repulsive interaction. In the coexistence phase where both components are superfluid, inter-species interactions induce a nondissipative drag between the two superfluid flows (Andreev-Bashkin effect). We show that this behavior leads to a modification of the usual Berezinskii-Kosterlitz-Thouless (BKT) transition in two dimensions. We extend the renormalization of the superfluid densities at finite temperature using the renormalization group approach and find that the vortices of one component have a large influence on the superfluid properties of the other, mediated by the nondissipative drag. The extended BKT flow equations indicate that the occurrence of the vortex unbinding transition in one of the components can induce the breakdown of superfluidity also in the other, leading to a locking phenomenon for the critical temperatures of the two gases.

Partial Fermionization: Spectral Universality in 1D Repulsive Bose Gases

Because of the vast growth of the many-body level density with excitation energy, its smoothed form is of central relevance for spectral and thermodynamic properties of interacting quantum systems. We compute the cumulative of this level density for confined one-dimensional continuous systems with repulsive short-range interactions. We show that the crossover from an ideal Bose gas to the strongly correlated, fermionized gas, i.e., partial fermionization, exhibits universal behavior: Systems with very few and up to many particles share the same underlying spectral features. In our derivation we supplement quantum cluster expansions with short-time dynamical information. Our nonperturbative analytical results are in excellent agreement with numerics for systems of experimental relevance in cold atom physics, such as interacting bosons on a ring (Lieb-Liniger model) or subject to harmonic confinement. Our method provides predictions for excitation spectra that enable access to finite-temperature thermodynamics in large parameter ranges.

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Using a coarse-grained molecular dynamics model, we simulate the self-assembly of PbSe nanocrystals (NCs) adsorbed at a flat fluid-fluid interface. The model includes all key forces involved: NC-NC short-range facet-specific attractive and repulsive interactions, entropic effects, and forces due to the NC adsorption at fluid-fluid interfaces. Realistic values are used for the input parameters regulating the various forces. The interface-adsorption parameters are estimated using a recently introduced sharp-interface numerical method which includes capillary deformation effects. We find that the final structure in which the NCs self-assemble is drastically affected by the input values of the parameters of our coarse-grained model. In particular, by slightly tuning just a few parameters of the model, we can induce NC self-assembly into either silicene-honeycomb superstructures, where all NCs have a {111} facet parallel to the fluid-fluid interface plane, or square superstructures, where all NCs have a {100} facet parallel to the interface plane. Both of these nanostructures have been observed experimentally. However, it is still not clear their formation mechanism, and, in particular, which are the factors directing the NC self-assembly into one or another structure. In this work, we identify and quantify such factors, showing illustrative assembled-phase diagrams obtained from our simulations. In addition, with our model, we can study the self-assembly dynamics, simulating how the NCs’ structures evolve from few-NCs aggregates to gradually larger domains. For example, we observe linear chains, where all NCs have a {110} facet parallel to the interface plane as typical precursors of the square superstructure, and zigzag aggregates, where all NCs have a {111} facet parallel to the interface plane as typical precursors of the silicene-honeycomb superstructure. Both of these aggregates have also been observed experimentally. Finally, we show indications that our method can be applied to study defects of the obtained superstructures.7 MoreReceived 28 October 2018Revised 28 January 2019DOI:https://doi.org/10.1103/PhysRevX.9.021015Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNanocrystalsPhysical SystemsNanoparticlesNanostructuresSuperlatticesPolymers & Soft MatterCondensed Matter, Materials & Applied Physics