Types Of Interaction Potentials Research Articles

Effect of electron–phonon interactions on a three-level QD-based spaser: linear and quadratic potentials

Abstract In this article, we study the effect of electron–phonon interaction on a spaser (surface plasmon amplification by stimulated emission of radiation) system consisting of a metal nanoparticle surrounded by a large number of quantum dots (QDs). Usually, the effect of electron–phonon interaction is neglected in the spaser-related literature. However, gain media, in this case QDs, attributed by the large Raman scattering cross-section, exhibit stronger electron–phonon interaction. In the present work, we investigate the effects of electron–phonon interaction on a three-level QD-based spaser. We consider two types of interaction potentials, linear and quadratic, and analyse their effects individually. First, we focus on the linear electron–phonon interaction that perturbs the electrons present in the excited state. This yields a periodic steady-state number of localized surface plasmons (LSPs). The accompanying analytic solution reveals that the population inversion of the gain medium depends on the linear potential strength (Frohlich constant) but does not affect the threshold of spaser considerably for the given numerical parameters. In addition to the LSP, phonons are generated during this process, the temporal dynamics of which are also presented here. Initially, the number of phonons exhibit decaying periodic oscillations, whose amplitude depends on the strength of the electron–phonon interaction. Under continuous pumping, at later times, the number of phonons reaches a steady-state value, which may find potential applications in the realization of continuous phonon nanolasers. Furthermore, the effect of the quadratic potential is investigated phenomenologically by increasing the excited-state decay rate. This results in numerous LSPs and an intense spaser spectrum.

Numerical study of the effect of particle size dispersion on order within colloidal assemblies

The formation of colloidal crystals is of interest in many fields, especially because of their optical properties. These properties are dictated by the colloidal arrangement. It is known that introducing particles with different sizes can change the structure of crystals and thus their resultant optical properties. To better understand how specific arrangements of particles can be obtained, a detailed understanding of the formation mechanisms is needed. The influence of particle size distribution on the formation of colloidal crystals is studied by means of Brownian dynamics simulations performed with different types of interaction potentials. Crystal formation is first analyzed in systems containing homogeneous particles, then in systems with a size distribution.It is shown that the interaction potential has a strong influence on the colloidal arrangement. For homogeneous particles, the width of the potential well affects the aggregate shape: a larger width leads to more elongated structures. When a size distribution is introduced, aggregation becomes more difficult since the number of isolated colloids increases, and aggregates become disordered regardless of the interaction potentials. Depending on the interaction potential, differences in the aggregates are observed. These differences are rationalized in terms of the specific features of the different potentials.

The Influence of the Effects of the Bound Electrons on the Ion Structural and Thermodynamic Properties

In this article, a strongly coupled one-component plasma (OCP), where ions interact with a background of weakly coupled electrons, is considered. The thermodynamic properties of this plasma were studied on the basis of three types of interaction potentials. The first potential with ionic core obtained from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ab initio$ </tex-math></inline-formula> simulations takes into account the effects of the bound electrons, the second is the well-known Yukawa potential, and the third is the effective potential derived by the method of dielectric response function taking into account electron screening and quantum-mechanical diffraction effect of electrons. The radial distribution functions (RDFs) were calculated for the first potential using molecular dynamics (MD) simulations and were additionally compared with the RDFs obtained for all three potentials by solving the integral Ornstein–Zernike equation in the hypernetted chain (HNC) approximation and show that the use of the effective potential is not applicable at warm dense matter (WDM) conditions, when the ion core is significant.

Deuteron-induced nonelastic cross sections based on the intranuclear cascade model with independent incident particles under interaction potentials

Deuteron-induced nonelastic cross sections are studied in an extended intranuclear cascade (INC) model. A three-body framework of proton, neutron, and target is introduced into the INC model to incorporate naturally the decomposition and capture reactions from weakly bound deuterons. This framework includes three types of interaction potential, namely proton-target, neutron-target, and proton-neutron, the last of which causes the two nucleons in the deuteron to oscillate and play an important role in its breakup. The calculated results reproduce well the experimental data for $^{12}\mathrm{C}, ^{40}\mathrm{Ca}, ^{58}\mathrm{Ni}$, and $^{208}\mathrm{Pb}$ targets with almost the same parameters as those determined previously for nucleon-induced nonelastic reactions. It is found that the contribution of the two-nucleon collision process increases with target size, that the contribution of the capture processes is limited to a narrow region at low energy for lighter targets, and that the contribution of the breakup process is relatively small compared to other processes. It is also concluded that discrete-level-constraint effects dominate in the low-energy region for light nuclei such as $^{12}\mathrm{C}$, while Coulomb effects dominate in the low-energy region for heavy nuclei. This result is consistent with the INC model of nucleon incidence, which explains well the nucleon-induced nonelastic cross sections at low energies.

Effective structure of a system with continuous polydispersity.

In a system of N particles, with continuous size polydispersity, there exists an N(N - 1) number of partial structure factors, making it analytically less tractable. A common practice is to treat the system as an effective one component system, which is known to exhibit an artificial softening of the structure. The aim of this study is to describe the system in terms of M pseudospecies such that we can avoid this artificial softening but, at the same time, have a value of M ≪ N. We use potential energy and pair excess entropy to estimate an optimum number of species, M0. We then define the maximum width of polydispersity, Δσ0, that can be treated as a monodisperse system. We show that M0 depends on the degree and type of polydispersity and also on the nature of the interaction potential, whereas Δσ0 weakly depends on the type of polydispersity but shows a stronger dependence on the type of interaction potential. Systems with a softer interaction potential have a higher tolerance with respect to polydispersity. Interestingly, M0 is independent of system size, making this study more relevant for bigger systems. Our study reveals that even 1% polydispersity cannot be treated as an effective monodisperse system. Thus, while studying the role of polydispersity by using the structure of an effective one component system, care must be taken in decoupling the role of polydispersity from that of the artificial softening of the structure.

Polymer-matrix stabilized metal nanoparticles: Synthesis, characterizations and insight into molecular interactions between metal ions, atoms and polymer moieties

Handling nanoparticles on a mesoscale order enhances the functionality of nanoparticles for high-end technological applications such as photonics, catalysis, biomedical applications, etc. In this context, polymer-metal hybrids have shown very popularity among material scientists in recent years where a suitable polymer matrix can be effectively used to stabilize nanoparticles through different mechanisms. The current paper deals with the synthesis of different types of hybrid particles of gold (Au), silver (Ag) and iron (Fe) using micron size carboxylic group functionalized Poly(N-isopropyl acrylamide) (PNIPAM) stimuli-responsive cross-linked microgels as micro-reactor in an in-situ approach. Transmission electron microscope (TEM) directly confirms the successful loading of metal nanoparticles within microgels and all the hybrid microgels have a narrow size distribution. Dynamic light scattering (DLS) measurement in the solution state shows that the swollen size of microgel-metal hybrid is comparatively smaller than that of pure microgels. UV-VIS spectroscopy strongly reveals the presence of plasmon peaks at 520 and 405 nm in case of gold and silver microgel hybrids respectively. In case of microgel-iron hybrids, the particles nicely respond to the applied magnetic field exerted by an external magnet and the effect is also reversible when the magnet is removed. Finally, to understand the type of molecular interaction that is responsible in holding the nanoparticles within the polymer matrices of microgels, we have carried out molecular docking between different metal ions (Au3+, Ag+, Fe2+) and atoms of gold, silver and iron (Au0, Ag0, Fe0) with the functional moieties (NIPAM monomer and carboxylate ion, COO−) of the polymer. Molecular docking studies with different types of interaction potentials (Van der Waals, hydrophobic, solvation, torsional and electrostatic) suggest that the electrostatic attraction dominates over all other potentials between positive metal ions and negative carboxylate ion (COO−) giving rise to the net binding energy of −9.28, −5.7, −1.46 kcal/mol for Fe2+, Au3+, and Ag+ respectively.

A novel linear elastic constitutive model for continuum-kinematics-inspired peridynamics

Javili et al. recently reported a continuum-kinematics-inspired peridynamic model, in which theoretical aspects regarding the balance of linear and angular momentum and other conservation principles are considered. However, the analytical formulation of the model constants and the microelastic potential energy functions and numerical implementation were not defined. In this paper, a novel linear elastic constitutive model is proposed for the continuum-kinematics-inspired peridynamics by introducing specific expressions for various interaction potentials. The one-neighbor interaction potential equivalent to conventional bond-based interaction potential is utilized to account for the constitutive relationship within line elements between two material points. In contrast, the two- and three-neighbor interaction potentials are employed to consider the areal and volumetric effects under general mechanical loads. Three relevant material parameters are introduced and derived from energy equivalence to a classical linear elastic continuum mechanics model. Equipped with the three types of interaction potentials, the novel continuum-kinematics-inspired peridynamics is extended from classical bond-based peridynamics, wherein the two interaction force vectors within a bond are unequal and not parallel to the bond direction, can be regarded as an alternative version of non-ordinary state-based peridynamics. The proposed model is numerically demonstrated to be effective in absolutely eliminating the restriction of the fixed Poisson’s ratio in classical bond-based peridynamics, notably improving the effectiveness of the other enriched bond-based peridynamics in reproducing the elastic deformation of solids subjected to heterogeneous deformation fields and completely removing the numerical oscillations in non-ordinary state-based peridynamics.

Realizing the Frenkel-Kontorova model with Rydberg-dressed atoms

We propose a method to realize the Frenkel-Kontorova model using an array of Rydberg dressed atoms. Our platform can be used to study this model with a range of realistic interatomic potentials. In particular, we concentrate on two types of interaction potentials: a springlike potential and a repulsive long-range potential. We numerically calculate the phase diagram for such systems and characterize the Aubry-like and commensurate-incommensurate phase transitions. Experimental realizations of this system that are possible to achieve using current technology are discussed.

First-principles melting of krypton and xenon based on many-body relativistic coupled-cluster interaction potentials

The solid-to-liquid phase transition for krypton and xenon is studied by means of parallel-tempering Monte Carlo simulations based on an accurate description of the atomic interactions within a many-body ansatz using relativistic coupled-cluster theory. These high-level data were subsequently fitted to computationally efficient extended Lennard-Jones and extended Axilrod-Teller-Muto types of interaction potentials. Solid-state calculations demonstrate that the many-body decomposition of the interaction energy converges well for the heavier rare gas solids, leading to solid-state properties in good agreement with experiment. The results show that it suffices to include two- and three-body interactions only for the melting simulation. The melting of the bulk is simulated for cells with cubic periodic boundary conditions, as well as within a finite cluster approach. For the latter, melting of spherical magic number clusters with increasing cluster size is studied, and the melting temperatures are obtained from extrapolation to the bulk. The calculated melting temperatures for the cluster extrapolation (the periodic approach values corrected for superheating are set in parentheses) are ${T}_{m}=113.7$ K (110.9 K) and ${T}_{m}=160.8$ K (156.1 K) for krypton and xenon, respectively. Both are in very good agreement with corresponding experimental values of 115.75 and 161.40 K.

Structural diversity of homobinuclear transition metal complexes of the phenazine ligand: theoretical investigation

DFT/BP86 calculations have been carried out on a series of hypothetical binuclear compounds of general formula (L3M)2(C12N2H8) (M = Sc–Ni, L3 = (CO)3, (PH3)3 and Cp−, and C12N2H8 = phenazine ligand-denoted Phn). The various structures with syn and anti configurations have been investigated, in order to determine the phenazine’s coordination to first-row transition metals of various spin states with syn and anti conformations. The lowest energy structures depend on the nature of the metal, the spin state, and the molecular symmetry. This study has shown that the electronic communication between the metal centers depends on their oxidation state and the attached ligands. The tricarbonyl and the triphosphine ligands gave rise to comparable results in terms of stability order of isomers, metal-metal bond distances, and the coordination modes. Metal-metal multiple bonding has been evidenced for Sc, Ti, and V complexes to compensate the electronic deficiency. The Cr, Mn, Fe, Co, and Ni-rich metals prefer the anti conformation due to the enhancement of the metal valence electron count. The spin density values calculated for the triplet and quintet spin structures point out that the unpaired electrons are localized generally on the metal centers. The Wiberg bond indices are used to evaluate the metal-metal bonding. Furthermore, calculations using the BP86-D functional which take into account the attractive part of the van der Waals type interaction potential between atoms and molecules that are not directly connected to each other gave comparable results to those obtained by BP86 functional in terms of coordination modes, HOMO-LUMO gaps, metal-metal bond orders, and the stability order between isomers, but with slight deviation of M–C, M–N, and M–M bond distances not exceeding 3%.

A Hard Convex Core Yukawa Equation of State for Nonassociated Chain Molecules

The compressibility factor of nonassociated chain molecules composed of hard convex core Yukawa segments was derived with SAFT-VR and an extension of the Barker-Henderson perturbation theory for convex bodies. The temperature-dependent chain and dispersion compressibility factors were derived using the Yukawa potential. The effects of temperature, packing fraction, and segment number on the compressibility factor were investigated for chains of the prolate sphereocylinder segments. A comparison of hard core Yukawa chain compressibility factor values and hard chain compressibility factor values showed that the type of interaction potential has more effect on those chain molecules with higher segment numbers. The results demonstrated that in reduced temperatures 1.4 and 2.4, the Yukawa chain of the compressibility factor is insensitive to temperature, while the dispersion term of the compressibility factor changes remarkably with the temperature. The derived equation of state can fairly predict the SAFT-VR results of the hard sphere core chain molecules in the limit of α = 1.

Entanglement creation in Compton scattering of neutrons on protons and its possible energetic consequences

It has been predicted that entanglement creation should be associated with a lowering of energy (as well as the well‐known decrease of entropy) for certain types of interaction potentials. This is a principally important question and it is shown here that np‐scattering has specific features that would make it suitable for experimental tests of this prediction using neutron scattering on hydrogen at high angles. For this purpose, the evolution of n‐p entanglement in Compton scattering on protons at epithermal energies (20–200 eV) is calculated over the separation distance 0–1 Å, corresponding to times up to 10−15 s after the collision. If an energy transfer is associated with the entanglement, it ought to be observable under these measurement conditions. © 2015 Wiley Periodicals, Inc.

Statistically interacting vacancy particles

The equilibrium statistical mechanics of one-dimensional lattice gases with interactions of arbitrary range and shape between first-neighbor atoms is solved exactly on the basis of statistically interacting vacancy particles. Two sets of vacancy particles are considered. In one set all vacancies are of one-cell size. In the other set the sizes of vacancy particles match the separation between atoms. Explicit expressions are obtained for the Gibbs free energy and the distribution of spaces between atoms at thermal equilibrium. Applications to various types of interaction potentials are discussed, including long-range potentials that give rise to phase transitions. Extensions to hard rod systems are straightforward and are shown to agree with existing results for lattice models and their continuum limits.

Thermal conductivity of BN-C nanostructures

Chemical and structural diversity present in hexagonal boron nitride ((h-BN) and graphene hybrid nanostructures provide new avenues for tuning various properties for their technological applications. In this paper we investigate the variation of thermal conductivity ($\kappa$) of hybrid graphene/h-BN nanostructures: stripe superlattices and BN (graphene) dots embedded in graphene (BN) are investigated using equilibrium molecular dynamics. To simulate these systems, we have parameterized a Tersoff type interaction potential to reproduce the ab initio energetics of the B-C and N-C bonds for studying the various interfaces that emerge in these hybrid nanostructures. We demonstrate that both the details of the interface, including energetic stability and shape, as well as the spacing of the interfaces in the material exert strong control on the thermal conductivity of these systems. For stripe superlattices, we find that zigzag configured interfaces produce a higher $\kappa$ in the direction parallel to the interface than the armchair configuration, while the perpendicular conductivity is less prone to the details of the interface and is limited by the $\kappa$ of h-BN. Additionally, the embedded dot structures, having mixed zigzag and armchair interfaces, affects the thermal transport properties more strongly than superlattices. Though dot radius appears to have little effect on the magnitude of reduction, we find that dot concentration (50% yielding the greatest reduction) and composition (embedded graphene dots showing larger reduction that h-BN dot) have a significant effect.

Interaction Potential between a Dislocation and a Pinning Atom in FCC Metals

Amplitude dependent internal friction (ADIF) was measured on 4N and 6N Cu crystals at 4K–40 K to study the interaction between a dislocation and a pinning atom. The temperature dependence of the stress amplitude necessary to produce a constant ADIF was well explained by assuming the Cottrell type interaction potential based on linear elasticity. This is clearly different from the case of Al crystals where it was necessary to consider a modified Cottrell potential including a deviation from linear elasticity near the dislocation center.

Effects of the interaction potential and hydrodynamic interaction on the diffusion-influenced reaction rates

Recently, we proposed an accurate analytic expression for the diffusive propagator of a pair of particles under a central interaction potential and hydrodynamic interaction, and derived the rate expressions for fully diffusion-controlled geminate and bimolecular reactions. In this work, we present a still more accurate propagator expression, and extend the theory to the partially diffusion-controlled cases with various types of interaction potentials, including the screened Coulomb potential and the potential of mean force due to solvation. We evaluate the accuracies of our theory and other competing theories against exact numerical results. It is shown that the improved rate expressions provide near exact results for most types of interaction potentials.

Trap with ultracold neutrons as a detector of dark matter particles with long-range forces

The possibility of using a trap with ultracold neutrons as a detector of dark matter particles with long-range forces is considered. The basic advantage of the proposed method lies in possibility of detecting the recoil energy 10-7 eV. The restrictions on parameters of Yukawa type interaction potential between dark matter particles and a neutron are presented for different dark matter densities on the Earth. The assumption concerned with long-range interaction of dark matter particles and ordinary matter leads to a substantial enhancement of cross section at low energy. Consequently, there arises a possibility of capture and accumulation of dark matter in a gravitational field of the Earth. Rough estimation of accumulation of low-energy dark matter on the Earth is discussed. The first experimental restrictions for existence of dark matter with long-range forces on the Earth are presented.

Simulation study of discotic molecules in the vicinity of the isotropic–liquid crystal transition

The equilibrium and microscopic properties of systems of discotic molecules have been investigated with Monte Carlo (MC) simulations. The study focuses on the behaviour of the fluid in the isotropic phase in the vicinity of the first liquid crystal transition, which involves either a nematic or a columnar phase. The molecules are modelled by rigid oblate spherocylinders with various types of interaction potentials. Molecular thickness/diameter ratios within L/D = 0.1–0.5 are considered. The MC equations of state are compared with theoretical predictions for hard convex bodies, based on molecular shape and virial expansions. A good agreement is found for the hard spherocylinder system, although discrepancies arise for L/D < 0.4 at sufficiently large packing fraction. Particular efforts are also devoted to characterising the formation of domains of stacked molecules in the isotropic phase for the different repulsive and attractive interaction models.

Local structures of fluid with discrete spherical potential: Theory and grand canonical ensemble Monte Carlo simulation

Grand canonical Monte Carlo simulation and theoretical calculations based on Ornstein-Zernike (OZ) integral equation and third order+second order perturbation density functional theory (DFT) are performed to study a system of spherical particles interacting through a core-softened (CS) potential combining a repulsive square soft core and an attractive square well. Both theoretical predictions and simulation results reveal peculiar homogeneous and inhomogeneous local structures originating from the discontinuous nature of the CS potential. The bulk radial distribution function displays discontinuities at the distances coinciding with the ranges of the successive repulsive and attractive parts in the CS potential function. The density profiles of confined CS fluid show the shapes arising from the complex interplay among the steric effects and the competition between the repulsive and attractive parts of the CS potential. Satisfactory agreement between the theoretical results and simulation data leads to the following conclusions: (i) a modified hypernetted chain approximation combined with a hard sphere bridge function, which has been recently proposed by one of the authors of this study, is sufficiently reliable for the structural studies of CS fluid, and (ii) the third order+second order perturbation DFT, which has proven successful for the study of inhomogeneous structure of model fluids with continuous intermolecular potential function, posses a high adaptability to be applied for various types of interaction potentials and performs well also in the case of discontinuous CS model.

Where are genes in paulingite? Mathematical principles of formation of inorganic materials on the atomic level

By means of the concept of universal optimum and general principles of inorganic gene, structures of paulingite-related zeolites and minerals have been constructed. The structures of zeolite Rho and paulingite are considered as members of zeolite family generated by the work of 4-colored cellular automaton (CA). The ideal symmetry of the members of the family is cubic, space group \( Im\overline{3}m \), a = 15 + 10n [A], where n is a number of the CA cycle (n = 0 for zeolite Rho and 2 for paulingite). A new hypothetical zeolite of the family with n = 1 is predicted and named ISC-1 (Institute of Silicate Chemistry-1); atomic coordinates and theoretical X-ray powder diffraction pattern have been calculated. It appears to be very probable that universal optimum contains all necessary information for its material realization (sharp configurations) and construction of materials with certain type of interaction potential (even with restrictions existing in theory for this potential).