Long-range Attractive Interactions Research Articles

Homogeneous crystallization in four-dimensional Lennard-Jones liquids.

We observe homogeneous crystallization in simulated high-dimensional (d>3) liquids that follow physically realistic dynamics and have system sizes that are large enough to eliminate the possibility that crystallization was induced by the periodic boundary conditions. Supercooled four-dimensional (4D) Lennard-Jones (LJ) liquids maintained at zero pressure and constant temperatures 0.59<T<0.63 crystallized within ∼2×10^{4}τ, where τ is the LJ time unit. Weeks-Chandler-Andersen (WCA) liquids that were maintained at the same densities and temperatures at which their LJ counterparts nucleated did not crystallize even after 2.5×10^{5}τ, showing that the presence of long-ranged attractive interactions dramatically speeds up 4D crystallization, much as it does in 3D. On the other hand, the overlap of the liquid and crystalline phases' local-bond-order distributions is smaller for LJ systems than for WCA systems, which is the opposite of the 3D trend. This implies that the widely accepted hypothesis that increasing geometrical frustration rapidly suppresses crystallization as the spatial dimension d increases is only generally valid in the absence of attractive interparticle forces.

Molecular Dynamics simulations and discrete perturbation theory for systems interacting via the parabolic-well pair potential

In this work, we performed Molecular Dynamics (MD) simulations to investigate the thermodynamic properties, including vapor pressures, critical points, pressure, excess energy, and vapor-liquid equilibrium, for a continuous version of the parabolic-well (PW) pair potential within the attractive range of 1.5 ≤λ≤3.0. In addition to conducting extensive MD simulations, we have developed an analytical equation of state for the Helmholtz free energy of particles interacting via the PW pair potential. This development was accomplished within the framework of discrete perturbation theory, involving discrete steps to accurately represent the general shape of the PW potential. Remarkably, our theoretical approach based on discrete perturbation theory demonstrates excellent agreement with MD simulations across a wide range of densities, temperatures, and pressures for the PW pair potential. Our findings demonstrate that PW fluids, characterized by long-range attractive interactions, deviate from the principle of corresponding states. However, for short-range attractive interactions, the fluids moderately follow the Ising universality class. Finally, the integration of discrete perturbation theory with MD simulations proves to be an efficient method for exploring the behavior of molecular fluids and colloidal systems.

Ligand coupling mechanism of the human serotonin transporter differentiates substrates from inhibitors

The presynaptic serotonin transporter (SERT) clears extracellular serotonin following vesicular release to ensure temporal and spatial regulation of serotonergic signalling and neurotransmitter homeostasis. Prescription drugs used to treat neurobehavioral disorders, including depression, anxiety, and obsessive-compulsive disorder, trap SERT by blocking the transport cycle. In contrast, illicit drugs of abuse like amphetamines reverse SERT directionality, causing serotonin efflux. Both processes result in increased extracellular serotonin levels. By combining molecular dynamics simulations with biochemical experiments and using a homologous series of serotonin analogues, we uncovered the coupling mechanism between the substrate and the transporter, which triggers the uptake of serotonin. Free energy analysis showed that only scaffold-bound substrates could initiate SERT occlusion through attractive long-range electrostatic interactions acting on the bundle domain. The associated spatial requirements define substrate and inhibitor properties, enabling additional possibilities for rational drug design approaches.

Magnon-magnon coupling mediated by topological edge states

The topology of the photonic bath shows excellent potential to engineer the intriguing interaction properties between light and matter. Here, we study the dielectric resonator array with a zigzag geometry, an analogy of the Su-Schrieffer-Heeger model equipped with peculiar freedom to manipulate the nearest-neighbor coupling strength by the internal interaction. A staggered coupling strength of s-type pillar modes is experimentally achieved via the photonic spin-orbit coupling by employing the zigzag dielectric resonator chain. As a result, we observe that the robust edge states of the zigzag chains manifest themselves with linear polarization for an even number of dielectric resonators but elliptical polarization for an odd number. In addition, by coupling magnons to the topological waveguide, we observe resonant magnon–magnon–edge-state coupling, whose coupling strength is topologically protected. More broadly, our work shows that topological waveguide-QED systems may provide the potential for synthesis and study of many-body states with attractive long-range interaction. Published by the American Physical Society 2024

Emergence of long-range attractive interactions between colloidal particles during curing of dispersion media.

Compared to traditional drying methods, curing processes result in lower emissions of volatile organic compounds and reduced energy consumption. Consequently, curing processes are widely used in the manufacturing of various polymer products, including inks, coatings, composites, and adhesives. In recent years, the functionality of these polymer products has been enhanced by incorporating colloids with antiviral and conductive properties. Despite the significant influence of colloidal arrangement on physical properties, the kinetics of colloidal particles during curing remains poorly understood. To explore the effective interactions between colloidal particles during curing, we investigated the dynamics of soft particles within dispersing media using molecular dynamics simulations. The likelihood of particle aggregation during curing significantly surpasses that of random contact. Our calculations reveal an effective potential, indicating a long-range attractive interaction between the large particles. This attraction results from the heterogeneity in the crosslink network of the dispersing media, distinguishing it from the classical depletion force. Since the structure of particle aggregation could be controlled by the interplay between curing rate and particle diffusion, our findings offer promising prospects for advancing the manufacturing processes of increasingly functional polymeric products.

Impact of long-range attraction on desorption kinetics.

Desorption of molecules from surfaces is widespread both in nature and technology. Despite its omnipresence and conceptual simplicity, fundamental details can be surprisingly complex and are often poorly understood. In many cases, first-order kinetics is assumed, which implies that the adsorbates do not interact with each other and desorption is the rate-limiting process. While this might be a good approximation in some cases, it is far from reality in the case of adsorbates that form ordered structures. Here, we study the desorption of a submonolayer film of 3-nitrophenol from the natural cleavage plane of calcite kept in ultrahigh vacuum. Interestingly, two distinctly different desorption regimes are observed during isothermal desorption monitored by dynamic atomic force microscopy. Initially, at high coverages, the coverage decreases almost linearly in time, indicating a constant desorption rate. Beyond this linear regime, at low coverages, a drastic increase in desorption rate is observed until the surface is completely empty. The transition between these two regimes is associated with a critical island width. We propose an existence of a long-range attractive interaction between the molecules as a possible explanation for the sudden increase in the desorption rate when a critical island width is reached. The herein observed phenomenon of two different desorption regimes is expected to be of general nature when interactions beyond next-neighbour attraction are present.

Nucleoside Analog Reverse-Transcriptase Inhibitors in Membrane Environment: Molecular Dynamics Simulations.

The behavior of four drugs from the family of nucleoside analog reverse-transcriptase inhibitors (zalcitabine, stavudine, didanosine, and apricitabine) in a membrane environment was traced using molecular dynamics simulations. The simulation models included bilayers and monolayers composed of POPC and POPG phospholipids. It was demonstrated that the drugs have a higher affinity towards POPG membranes than POPC membranes due to attractive long-range electrostatic interactions. The results obtained for monolayers were consistent with those obtained for bilayers. The drugs accumulated in the phospholipid polar headgroup region. Two adsorption modes were distinguished. They differed in the degree of penetration of the hydrophilic headgroup region. Hydrogen bonds between drug molecules and phospholipid heads were responsible for adsorption. It was shown that apricitabine penetrated the hydrophilic part of the POPC and POPG membranes more effectively than the other drugs. Van der Waals interactions between S atoms and lipids were responsible for this.

Primordial black holes as a dark matter candidate in theories with supersymmetry and inflation

We show that supersymmetry and inflation, in a broad class of models, generically lead to formation of primordial black holes (PBHs) that can account for dark matter. Supersymmetry predicts a number of scalar fields that develop a coherent condensate along the flat directions of the potential at the end of inflation. The subsequent evolution of the condensate involves perturbative decay, as well as fragmentation into Q-balls, which can interact by some long-range forces mediated by the scalar fields. The attractive scalar long-range interactions between Q-balls facilitates the growth of Q-balls until their ultimate collapse to black holes. For a flat direction lifted by supersymmetry breaking at the scale Λ ∼ 100 TeV, the black hole masses are of the order of (M 3 Planck/Λ2) ∼ 1022 g, in the allowed range for dark matter. Similar potentials with a lower scale Λ (not necessarily associated with supersymmetry) can result in a population of primordial black holes with larger masses, which can explain some recently reported microlensing events.

Dynamics of Target DNA Binding and Cleavage by Staphylococcus aureus Cas9 as Revealed by High-Speed Atomic Force Microscopy.

Programmable DNA binding and cleavage by CRISPR-Cas9 has revolutionized the life sciences. However, the off-target cleavage observed in DNA sequences with some homology to the target still represents a major limitation for a more widespread use of Cas9 in biology and medicine. For this reason, complete understanding of the dynamics of DNA binding, interrogation and cleavage by Cas9 is crucial to improve the efficiency of genome editing. Here, we use high-speed atomic force microscopy (HS-AFM) to investigate Staphylococcus aureus Cas9 (SaCas9) and its dynamics of DNA binding and cleavage. Upon binding to single-guide RNA (sgRNA), SaCas9 forms a close bilobed structure that transiently and flexibly adopts also an open configuration. The SaCas9-mediated DNA cleavage is characterized by release of cleaved DNA and immediate dissociation, confirming that SaCas9 operates as a multiple turnover endonuclease. According to present knowledge, the process of searching for target DNA is mainly governed by three-dimensional diffusion. Independent HS-AFM experiments show a potential long-range attractive interaction between SaCas9-sgRNA and its target DNA. The interaction precedes the formation of the stable ternary complex and is observed exclusively in the vicinity of the protospacer-adjacent motif (PAM), up to distances of several nanometers. The direct visualization of the process by sequential topographic images suggests that SaCas9-sgRNA binds to the target sequence first, while the following binding of the PAM is accompanied by local DNA bending and formation of the stable complex. Collectively, our HS-AFM data reveal a potential and unexpected behavior of SaCas9 during the search for DNA targets.

Channel-lipid interactions drive the emergence of ion channel clustering, channel-channel cooperativity, and activation hysteresis.

The activation of voltage gated ion channels has been intensely investigated for decades and it is now so well characterized that we have an atomically-detailed description of the major conformational changes taking place at the level of the single molecule. However, this accurate picture cannot accommodate recent experimental observations that highlight a dramatic and so far unsuspected collective behavior: voltage gated ion channels in physiological membranes form clusters and gate cooperatively. Here we present a quantitative theory that bridges these two vastly different length scales and reconciles these seemingly conflicting views. This novel conceptual framework, which is rooted in the statistical physics of immiscible fluids, accounts for the formation of lipid rafts and for the bias they entail on the conformation of the residing ion channels. First, we use tens-of-microseconds MARTINI simulations to show that annular lipids have a distinct compositional bias, which is different for the resting and the activated states. We then use these simulations to estimate channel-lipid interactions and thus parametrize a mesoscopic model. This allows us to explore the spatial organization of ion channels and their response (in the time domain) to changes in the transmembrane potential. We find that channels embedded in membranes close to a miscibility transition develop attractive long-range interactions that give rise to clustering effects. Strikingly, the lipid phase behavior is itself affected by the activation state of the ion channels. Finally, we observed strong activation cooperativity and long time-scales hysteresis effects which can potentially explain the modal gating phenomena observed in many single channel recordings.

Modified Thirring model beyond the excluded-volume approximation

Long-range interacting systems may exhibit ensemble inequivalence and can possibly attain equilibrium states under completely open conditions, for which energy, volume and number of particles simultaneously fluctuate. Here we consider a modified version of the Thirring model for self-gravitating systems with attractive and repulsive long-range interactions in which particles are treated as hard spheres in dimension d = 1, 2, 3. Equilibrium states of the model are studied under completely open conditions, in the unconstrained ensemble, by means of both Monte Carlo simulations and analytical methods and are compared with the corresponding states at fixed number of particles, in the isothermal-isobaric ensemble. Our theoretical description is performed for an arbitrary local equation of state, which allows us to examine the system beyond the excluded-volume approximation. The simulations confirm the theoretical prediction of the possible occurrence of first-order phase transitions in the unconstrained ensemble. This work contributes to the understanding of long-range interacting systems exchanging heat, work and matter with the environment.

Superconductivity from energy fluctuations in dilute quantum critical polar metals

Superconductivity in low carrier density metals challenges the conventional electron-phonon theory due to the absence of retardation required to overcome Coulomb repulsion. Here we demonstrate that pairing mediated by energy fluctuations, ubiquitously present close to continuous phase transitions, occurs in dilute quantum critical polar metals and results in a dome-like dependence of the superconducting Tc on carrier density, characteristic of non-BCS superconductors. In quantum critical polar metals, the Coulomb repulsion is heavily screened, while the critical transverse optical phonons decouple from the electron charge. In the resulting vacuum, long-range attractive interactions emerge from the energy fluctuations of the critical phonons, resembling the gravitational interactions of a chargeless dark matter universe. Our estimates show that this mechanism may explain the critical temperatures observed in doped SrTiO3. We provide predictions for the enhancement of superconductivity near polar quantum criticality in two- and three-dimensional materials that can be used to test our theory.

Anticlinic order of long-range repulsive rodlike magnetic particles in two dimensions

In the field of liquid crystals, it is well known that rodlike molecules interacting via long-range attractive interactions or short-range repulsive potentials can exhibit orientational order. In this work, we are interested in what would happen to systems of rodlike particles interacting via a long-range repulsive potential. In our model, each particle consists of a number of point dipoles uniformly distributed along the particle length, with all dipoles pointing along the z axis so that the rodlike particles repel each other when they lie in the x-y plane. Dipoles from different particles interact via an r^{-3} potential, where r is the distance between the dipoles. We have considered two model systems, each with N particles in a unit cell with periodic boundary conditions. In the first, particle centers are fixed on a square or triangular lattice but they are free to rotate. In the second, particles are free to translate as well as rotate in cells with variable shapes. Here they self-assemble to form configurations where the stress tensors are isotropic. Our numerical results show that, at low temperatures, the particles tend to form stripes with alternating orientations, resembling herringbone patterns or the anticlinic Sm-C_{A} liquid crystal phase.

Revisiting Anderson-Higgs mechanism: application of Lieb-Schultz-Mattis theorem

We consider an electron model of superconductivity on a three-dimensional lattice where there are on-site attractive Hubbard interaction and long-range repulsive Coulomb interaction. It is claimed that fully gapped s-wave superconductivity within this model, if present, exhibits spontaneous translation symmetry breaking possibly related to a charge order. Our discussions are based on an application of the Lieb-Schultz-Mattis theorem under some physical assumptions. The inconsistency between the proposed supersolid and experiments can impose some constraints on a reasonable choice of a theoretical model.

Phonon-Mediated Long-Range Attractive Interaction in One-Dimensional Cuprates.

Establishing a minimal microscopic model for cuprates is a key step towards the elucidation of a high-T_{c} mechanism. By a quantitative comparison with a recent insitu angle-resolved photoemission spectroscopy measurement in doped 1D cuprate chains, our simulation identifies a crucial contribution from long-range electron-phonon coupling beyond standard Hubbard models. Using reasonable ranges of coupling strengths and phonon energies, we obtain a strong attractive interaction between neighboring electrons, whose strength is comparable to experimental observations. Nonlocal couplings play a significant role in the mediation of neighboring interactions. Considering the structural and chemical similarity between 1D and 2D cuprate materials, this minimal model with long-range electron-phonon coupling will provide important new insights on cuprate high-T_{c} superconductivity and related quantum phases.

Higgs mode stabilization by photoinduced long-range interactions in a superconductor

We show that low-lying excitations of a 2D BCS superconductor are significantly altered when coupled to an externally driven cavity, which induces controllable long-range attractive interactions between the electrons. We find that they combine non-linearly with intrinsic local interactions to increase the Bogoliubov quasiparticle excitation energies, thus enlarging the superconducting gap. The long-range nature of the driven-cavity-induced attraction qualitatively changes the collective excitations of the superconductor. Specifically, they lead to the appearance of additional collective excitations of the excitonic modes. Furthermore, the Higgs mode is pushed into the gap and now lies below the Bogoliubov quasiparticle continuum such that it cannot decay into quasiparticles. This way, the Higgs mode's lifetime is greatly enhanced.

A reaction–diffusion particle model for clustering of self-propelled oil droplets on a surfactant solution

We experimentally and numerically investigate collective behaviors of oil droplets floating on a surfactant solution in a narrow circular channel. A closed environment where a glass cover is placed on the channel shown that ethyl salicylate droplets on the surface of sodium dodecyl sulfate solution exhibit transient oscillatory dynamics, leading to the formation of a single cluster via the merging of sub-clusters. When the glass cover is removed, oscillatory behavior resumes, and the cluster breaks up. To understand these experimental findings, we introduce a mathematical model that combines equations of motion for droplets with a reaction–diffusion system, where droplet dynamics and the chemical reactions are considered on the one-dimensional surface, and the diffusion of chemicals in the air phase and the water phase is treated in the two-dimensional region. Our model successfully reproduces transient oscillations and the characteristics of cluster formation, and the effect of the glass cover. We argue that the attractive long-range interaction due to the global concentration profile of the solution suffices for the cluster formation.

Three-dimensional ferromagnetism and magnetotransport in van der Waals Mn-intercalated tantalum disufide

Van der Waals (vdW) ferromagnets are an important class of materials for spintronics applications. The recent discovery of atomically vdW magnets CrI$_3$ and Cr$_2$Ge$_2$Te$_6$ has triggered a renaissance in the area of two-dimensional (2D) magnetism. Herein we systematically studied 2H-Mn$_{0.28}$TaS$_2$ single crystal, a 2D vdW ferromagnet with $T_c$ $\sim$ 82.3 K and a large in-plane magnetic anisotropy. Mn $K$-edge x-ray absorption spectroscopy was measured to provide information on its electronic state and local atomic environment. The detailed magnetic isotherms measured in the vicinity of $T_c$ indicates that the spin coupling inside 2H-Mn$_{0.28}$TaS$_2$ is of a three-dimensional (3D) Heisenberg-type coupled with the attractive long-range interaction between spins that decay as $J(r)\approx r^{-4.85}$. Both resistivity $\rho(T)$ and thermopower $S(T)$ exhibit anomalies near $T_c$, confirming that the hole-type transport carriers strongly interact with local moments. An unusual angle-dependent magnetoresistance is further observed, suggesting a possible field-induced novel magnetic structure.

Temperature dependence of the rate coefficient of formation of CN radical from C + NH

Rate coefficients of the complex-forming C + NH→H + CN reaction have been calculated at temperatures ranging from 5 K to 800 K using quasi-classical trajectories on a potential energy surface which accurately describes the attractive long-range interaction, along with results using two capture models. In contrast with the constant value recommended in astrochemical databases, a steep decrease of the rates has been found up to 150 K, and then they tends to be nearly constant. Such behavior is analyzed in terms of the rovibrational state-selected rate coefficients and cross sections singling out the role played by the rotational excitation of the initial diatom. The effect of the electronic degeneracy is also discussed.

Long-Range Surface-Assisted Molecule-Molecule Hybridization.

Metalated phthalocyanines (Pc's) are robust and versatile molecular complexes, whose properties can be tuned by changing their functional groups and central metal atom. The electronic structure of magnesium Pc (MgPc)-structurally and electronically similar to chlorophyll-adsorbed on the Ag(100) surface is investigated by low-temperature scanning tunneling microscopy and spectroscopy, non-contact atomic force microscopy, and density functional theory. Single, isolated MgPc's exhibit a flat, fourfold rotationally symmetric morphology, with doubly degenerate, partially populated (due to surface-to-molecule electron transfer) lowest unoccupied molecular orbitals (LUMOs). In contrast, MgPc's with neighbouring molecules in proximity undergo a lift of LUMOs degeneracy, with a near-Fermi local density of states with reduced twofold rotational symmetry, indicative of a long-range attractive intermolecular interaction. The latter is assigned to a surface-mediated two-step electronic hybridization process. First, LUMOs interact with Ag(100) conduction electrons, forming hybrid molecule-surface orbitals with enhanced spatial extension. Then, these delocalized molecule-surface states further hybridize with those of neighbouring molecules. This work highlights how the electronic structure of molecular adsorbates-including orbital degeneracies and symmetries-can be significantly altered via surface-mediated intermolecular hybridization, over extended distances (beyond 3nm), having important implications for prospects of molecule-based solid-state technologies.