First-neighbor Interaction Research Articles

Edge Magnetism in MoS2 Nanoribbons: Insights from a Simple One-Dimensional Model.

Edge magnetism in zigzag nanoribbons of monolayer MoS2 has been investigated with both density functional theory and a tight-binding plus Hubbard (TB+U) Hamiltonian. Both methods revealed that one band crossing the Fermi level is more strongly influenced by spin polarization than any other bands. This band originates from states localized on the sulfur edge of the nanoribbon. Its dispersion closely resembles that of the energy branch obtained in a linear chain of atoms with first-neighbor interaction. By exploiting this resemblance, a toy model has been designed to study the energetics of different spin configurations of the nanoribbon edge.

Critical exponents of master-node network model.

The dynamics of competing opinions in social network plays an important role in society, with many applications in diverse social contexts such as consensus, election, morality, and so on. Here, we study a model of interacting agents connected in networks in order to analyze their decision stochastic process. We consider a first-neighbor interaction between agents in a one-dimensional network with the shape of ring topology. Moreover, some agents are also connected to a hub, or master node, who has preferential choice or bias. Such connections are quenched. As the main results, we observed a continuous nonequilibrium phase transition to an absorbing state as a function of control parameters. By using the finite-size scaling method we analyzed the static and dynamic critical exponents to show that this model probably cannot match any universality class already known.

Theoretical investigation of phonon modes related to first Brillouin zone centre and properties of double perovskites Ba2MWO6 (M=Mg, Zn, Cd)

In this research work, we investigate phonon modes related to the first Brillouin zone centre of double perovskites Ba2MgWO6, Ba2ZnWO6, and Ba2CdWO6. Besides, Debye temperature, elastic constants, and elastic properties are also evaluated. These investigations are carried out by employing a theoretical model based on the six parameters bond-bending force constant. From our calculations, we found the strength of the first-neighbor interaction is higher as compared to the second and third neighbor's interatomic interactions. Our computed results corresponding to Young, Bulk, and Shear moduli and Debye temperature are found in a sequence Ba2CdWO6>Ba2ZnWO6>Ba2MgWO6. Moreover, all the examined double perovskite compounds reveal their ductile and elastically anisotropic nature. Our predicted results for frequencies of zone-centre phonons and elastic constants also show nice agreement with previously reported results.

Thermally driven state in a spin-1 model with competing interactions

We study a recently proposed spin-1 model with competing antiferromagnetic first-neighbor interaction and a third-neighbor coupling mediated by nonmagnetic states, which reproduces topological features of the phase diagrams of high-T_{c} superconductors [S. A. Cannas and D. A. Stariolo, Phys. Rev. E 99, 042137 (2019)2470-004510.1103/PhysRevE.99.042137]. We employ a cluster mean-field approach to investigate effects of crystal field anisotropy on the phase transitions hosted by this model. At low temperatures, the temperature-crystal field phase diagram exhibits superantiferromagnetic (SAF), antiferromagnetic (AF), and paramagnetic (PM) phases. In addition, we found a thermally driven state between SAF and PM phases. This thermally driven state and the SAF phase appears in the phase diagram as a domelike structure. Our calculations indicate that only second-order phase transitions occur in the PM-AF phase boundary, as suggested by previous Monte Carlo simulations.

Effect of solute-solute interactions on strengthening of random alloys from dilute to high entropy alloys

The yield strength of random metal alloys, i.e. alloys with random occupation of the crystalline lattice sites by the elemental constituent atoms all considered as solutes, is primarily understood as controlled by solute/dislocation interactions. Solute-solute interactions exist and provide the energetic driving force for both short-range and long-range order but can then also affect yield strength even in the random alloy. Here, a recent theory for random alloys is extended to include solute-solute interactions described by pair-wise interactions. The new theory involves the standard deviation in total solute-solute interaction energies as a dislocation segment glides through the material, which changes specific solute-solute pairs across the glide plane at every pair distance. An analytic expression is derived for the above standard deviation and validated against numerical simulations on a wide range of model random alloys consisting of 2–5 elements interacting via Lennard–Jones pair potentials. The theory is applied to the bcc MoNbTaW high entropy alloy, using solute-solute interactions computed via first-principles, and a model NbTaV alloy, described by EAM potentials, where the strength increases negligibly by 2% and 0.45%, respectively. Application to random dilute fcc Ni-Al, where the first-neighbor Al-Al interaction is very strongly repulsive, shows significant strengthening of 60–100% at 10% Al, depending on the origin of the inputs. Some connections to literature atomistic simulations on Ni–Al are also presented. Overall, the present theory provides a quantitative framework for assessing the relative roles of solute-dislocation and solute-solute interactions on strengthening in random alloys.

Hamiltonian short-time critical dynamics of the three-dimensional XY model.

The short-time relaxation critical behavior of the XY model on a simple-cubic lattice is investigated within the scope of deterministic Hamiltonian dynamics. The Hamiltonian includes a first-neighbor interaction between planar vectors and a rotational kinetic term from which the motion equations are derived. The dynamical evolution from a fully ordered initial state is followed by employing a symplectic algorithm based on a high-order Trotter-Suzuki decomposition of the time-evolution operator. A finite-time scaling analysis is performed to provide accurate estimates of the critical energy density, the order-parameter relaxation exponent, and the dynamical critical exponent. The estimated critical exponents are consistent with prior theoretical and experimental values reported for the superfluid ^{4}He, extreme type-II superconducting, and Bose-Einstein condensation transitions.

Vibrational and elastic properties of silicate spinels A2SiO4 (A = Mg, Fe, Ni, and Co)

A six-parameter bond-bending force constant model is used to calculate the zone-center (Γ = 0) Raman and infrared phonon mode frequencies, elastic constants and related properties, the Debye temperatures, and sound velocities along high-symmetry directions for A2SiO4 (A = Mg, Fe, Ni, and Co) spinels. The main outcomes of the calculations are that the interactions between Si and O atoms (first-neighbor interaction) are stronger than those between A and Oatoms (A = Mg, Fe, Ni, and Co) (second-neighbor interaction). The elastic constants C11, C12, and C44 decrease in the order Mg > Fe > Ni > Co. The calculated bulk modulus, Poisson's ratio, and anisotropy decrease in the sequence Fe2SiO4 → Ni2SiO4 → Co2SiO4 → Mg2SiO4. On comparison, we find overall good agreement with the available experimental and previously calculated data.

Theoretical investigation of the influence of reaction and diffusion kinetics upon thin-film reactive diffusion

Atomistic kinetic Monte Carlo simulations, considering the thermodynamic model of the nonregular solid solution on a rigid fcc lattice and using the first-neighbor atomic pair interaction Ising model, were performed to investigate the influence of reaction and diffusion kinetics on thin-film reactive diffusion with a semi-infinite substrate. The simulations show that compound bulk energies have no effect on the phase sequence of appearance during sequential phase formation. However, a diffusion asymmetry between the elements composing the solid solution has a strong effect on sequential phase formation. Diffusion asymmetry increases the critical thickness of the simultaneous-to-sequential phase formation transition, modifies the phase formation sequence, and controls which phase is the first to form. Asymmetrical diffusion can promote transient phase formation and can prevent some phases of the bulk phase diagram from forming. In addition, it influences the thicknesses of phases and their lifetimes during thin-film reactive diffusion. Consequently, the control of atom diffusion during reactive diffusion, for example, thanks to the controlled introduction of impurities, should allow the phase formation sequence of a given binary system to be modified.

Dimer adsorption on square surfaces with first- and second-neighbor interactions

Dimer adsorption on surfaces simulates the adsorption of particles that bind onto two nearest-neighbor sites. In 1993, we constructed a transfer matrix ( T-matrix) for the study of dimers on stepped surfaces, consisting of M-sites wide square terraces, considering only first-neighbor interaction energies. Here, we consider a more realistic model by including both first- and second-neighbor interaction energies, V and W. The non-trivial construction of the T-matrix to include second-neighbor interactions is used to obtain the low-temperature energy phase diagrams of the dimer system for any M, when first-neighbors are attractive, and for values of M < 7 when first-neighbors are repulsive. New crystallization patterns and phases are observed and extrapolated to infinite M. Monte Carlo simulation techniques confirm our T-matrix results, but the T-matrix method is found to be computationally more efficient and more precise. However, Monte Carlo parallel tempering simulations combined with finite-size scaling, while limited in precision, are more efficient to obtain the critical temperature of the various order–disorder transitions as a function of W / | V | , from the study of the heat capacity and the order parameter as functions of temperature. We also discuss the relevance of these results to experiments.

Magnetic structure and enhancedTNof the rare-earth intermetallic compoundTbRhIn5: Experiments and mean-field model

In this work the physical properties of the intermetallic compound $\mathrm{Tb}\mathrm{Rh}{\mathrm{In}}_{5}$ were investigated by means of temperature-dependent magnetic susceptibility, electrical resistivity, heat-capacity, and resonant x-ray magnetic diffraction experiments. $\mathrm{Tb}\mathrm{Rh}{\mathrm{In}}_{5}$ is an intermetallic compound that orders antiferromagnetically at ${T}_{N}=45.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the highest ordering temperature among the existing $R\mathrm{Rh}{\mathrm{In}}_{5}$ (1-1-5, $\mathrm{R}=\mathrm{rare}$ earth) materials, which in contrast to what is expected from a de Gennes scaling along the $R\mathrm{Rh}{\mathrm{In}}_{5}$ series. The x-ray resonant diffraction data have allowed us to solve the magnetic structure of $\mathrm{Tb}\mathrm{Rh}{\mathrm{In}}_{5}$. Below ${T}_{N}$, we found a commensurate antiferromagnetic structure with a propagation vector $(1∕2,0,1∕2)$ and the Tb moments oriented along the $c$ axis. Strong (over two orders of magnitude) dipolar enhancements of the magnetic Bragg peaks were observed at both Tb absorption edges ${L}_{\mathit{II}}$ and ${L}_{\mathit{III}}$, indicating a fairly high polarization of the Tb $5d$ levels. Using a mean-field model including an isotropic first-neighbor exchange interaction $({J}_{R\text{\ensuremath{-}}R})$ and the tetragonal crystalline electrical field (CEF), we evaluate the influence of the CEF effects in the physical properties of $\mathrm{Tb}\mathrm{Rh}{\mathrm{In}}_{5}$. The results reported here seem to corroborate a general trend of CEF-driven effects on ${T}_{N}$ along the $R\mathrm{Rh}{\mathrm{In}}_{5}$ series.

Magnetic neutron scattering measurements on a single crystal of frustratedZnFe2O4

Single crystals of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ are investigated with neutron scattering measurements from the viewpoint of geometrical frustration. Magnetic diffuse scattering was distributed along the first Brillouin zone boundary of the fcc structure. The results show that the frustration occurs between the antiferromagnetically coupled third-neighbor spins, rather than between the similarly coupled first-neighbor spins. In addition, another type of diffuse scattering was found around some nuclear Bragg peak positions. This indicates that the first-neighbor exchange interaction in the 90\ifmmode^\circ\else\textdegree\fi{} configuration is ferromagnetic rather than antiferromagnetic. Energy spectra were investigated at several points. The unusual magnetic behavior originates from the geometrical frustration and a unique property of the first-neighbor interaction.

A two-dimensional spin model of Al/Si order in feldspars: visualization of short-range and long-range order

Ordering schemes analogous to the Al,Si ordering in albite and anorthite are simulated using a two-dimensional spin model. Equilibrium calculations are performed using the square approximation of the cluster variation method. A stochastic algorithm is developed to visualize ordering patterns and domain textures of typical Al,Si configurations with short- and long-range order. At the rather low Al/Si ratio of albite a high degree of short-range order (SRO) is expected as a consequence of strong interaction within first-neighbour Al,Si pairs. At a higher Al/Si ratio of anorthite long-range order (LRO) of anorthite-type appears to be a better alternative to the SRO. The SRO/LRO transition occurs due to the destabilization of anti-phase boundaries between short-range ordered domains. LRO of albite-type is stabilized mainly by the interaction within second-neighbour Al,Si pairs, which is less strong in comparison to the first-neighbor interaction.

Theoretical studies on the iminium ion-forming reaction

The iminium ion forming reactions of YC6H4NHCH2NH3+(I) and the corresponding carbon analog, YC6H4CH2CH2NH3+ (II) were studied theoretically at the MP2/6–31G*//RHF/6–31G* level. The iminium ion-forming reactions are favored mainly due to a large amount of electron donation (0.05–0.06e) from the nitrogen to the antibonding orbital of the cleaving bond, nN σ*(r3), by a first-neighbor vicinal charge-transfer interaction. At ca 50% progress of reaction, i.e. bond cleavage in the SN1 transition state (TS), bond contraction of the geminal bond (r2) is greater by ca 10% (60%), which is also greater than bond stretching of a vicinal bond (50%). The reaction through the imbalanced TS provides the minimum energy path in accordance with the basic laws of nature. The Hammett ρ values for the iminium ion-forming activation and equilibrium processes are ca −1.3 and −4.3, respectively. The negative activation energies for the SN2 processes with I in the gas phase are consistent with the experimental direct nucleophilic displacement by a strong nucleophile at the iminium ion-forming substrate in water. Copyright © 1999 John Wiley & Sons, Ltd.

Coadsorption of two monomer species on a square lattice with first- and second-neighbor interactions

We obtain the low-temperature phases and phase transitions of the coadsorption of two monomer species on a semi-infinite square lattice of odd width M, with first- and second-neighbor interactions. We study the cases for which first-neighbor interactions between two monomers of the same species are repulsive, allowing all other interactions to be attractive or repulsive. Most of the numerical results are found to fit exact closed-form expressions in M, thus allowing exact analytic extrapolations to the infinite two-dimensional case (M5‘). @S1063-651X~97!05508-6# While no exact solution of lattice models for the adsorption or coadsorption of gas molecules on surfaces has been analytically derived, when first- and second-neighbor interactions between the adsorbed molecules are considered, lowtemperature numerical studies of one species of monomers adsorbed on a square lattice allow one to obtain closed-form analytic expressions for all possible phases and for the conditions under which phase transitions occur @1#. In this previous work, the surface considered was a semi-infinite M3N square lattice ( N!‘) in the presence of a gas containing one molecular species, with the adsorbed molecules each occupying one site. For this reason, we referred to them as monomers. The system is at thermal equilibrium with the monomer chemical potential energy m depending on the external gas pressure. The interaction energies of an adsorbed monomer are V0 with the lattice, V with any first-neighbor monomer at a distance a, and W with any second-neighbor monomer at a distance a&. The assumption was that the first-neighbor interaction is repulsive, V,0, allowing the second-neighbor interaction to be either attractive or repulsive. The study showed six distinct interaction regions with ‘‘p phases’’ appearing sequentially with increasing external pressure, from the empty lattice phase p0 to the fully covered lattice phase p 15 , as follows @1#.

Kinetic model for a polymer in one dimension.

We consider a model for a directed polymer on a one-dimensional lattice of width 2, with attractive interactions between monomers that occupy first-neighbor sites on the lattice and are not consecutive along the chain. We show that this model is equivalent to the one-dimensional Ising model with first- and second-neighbor interactions. We study the kinetic behavior of the model in the region of the phase diagram where the ground state is not frustrated, using a Glauber ansatz for the time evolution of the configurations. In order to decouple the dynamical equations, we use the pair approximation. In this approximation, we show that the dynamical exponent of the model is a function of the ratio between second- and first-neighbor interaction strengths. (c) 1995 The American Physical Society

Orientational phases for M3C60.

The mechanism of the orientational ordering of ${\mathrm{C}}_{60}$ in alkali-metal-doped fullerenes ${\mathit{M}}_{3}$${\mathrm{C}}_{60}$ is studied. Since the M-${\mathrm{C}}_{60}$ (M=K,Rb) interactions cause the ${\mathrm{C}}_{60}$ molecules to assume one of two standard orientations, this model is equivalent to a generalized Ising model on a fcc lattice. The Ising interactions depend on two type of energies: (1) the direct interaction, i.e., the orientationally dependent part of interactions between nearest-neighboring ${\mathrm{C}}_{60}$ molecules (each carrying charge -$3e$), and (2) the band energy of the electrons transferred from ${\mathit{M}}^{+}$ ions to the ${\mathrm{C}}_{60}^{\mathrm{\ensuremath{-}}3}$ ions. It is shown that the contribution to the pairwise interaction from the direct orientational interaction is ferromagnetic and dominantly nearest neighbor. However, contributions from the band (kinetic) energy of the conduction electrons are found to be antiferromagnetic for first- and third-nearest neighbors, ferromagnetic for second- and fourth-nearest neighbors, and negligible for further neighbors. The total first-neighbor interaction is probably antiferromagnetic. a non-negligible four-spin interaction is also obtained. The implication of these results for the orientational structure is discussed.

Antiferromagnetic coupling between the Mn and Fe nearest neighbours in ferromagnetic Mn:Pt-10 at.% Fe

The low-temperature nuclear orientation of 54Mn in ferromagnetic Pt-10 at.% Fe has been studied in the temperature range 4-50 mK and in the external magnetic field range 0.5-8.5 T. Considerable noncollinearity of Mn magnetic moments with respect to the bulk magnetization direction has been found in the whole Bext range. A model based on the Heisenberg Hamiltonian in the first-neighbour approximation is proposed, which fully describes the experimental data. The authors found that the first-neighbor Mn-Fe exchange interaction is antiferromagnetic with the value JMn-Fe=-21(1) K, which lies in the range of the nearest-neighbor Mn-Mn or Fe-Fe exchange interaction parameters for Pt-based alloys.

π-electron calculations of polarizabilities in conjugated systems

Finite-field technique has been applied to the calculation of π molecular polarizabilities within the Pariser–Parr–Pople Hamiltonian. This formalism allows to analyze large oligomers containing up to 400 atoms, and asymptotic behaviors may be attained in some cases. We have investigated the role of the polymer size, the backbone geometries, the presence of neutral and charged defects (solitons, polarons, bipolarons), the chemical nature of the monomeric unit on the polarizabilities. Generally, the polarizabilities are not deeply modified by a change of the geometrical characteristics, and may lead to huge values for sufficiently large chains. Besides, the charge of the system is the leading factor which determines the values of this property. The evolution of the polarizability with the number N of π atomic centers, αu depends largely on the charge, and on the defect. For the neutral systems, the polarizability per monomeric unit αu increases smoothly, and then exhibits an asymptotic behavior with N. For polymers with a defect, this variation is different: αu first increases with N, reaches a maximum αu max for Nmax, and finally tends to an asymptotic value. The values of αu max for Nmax depend on the type of defect (soliton vs polaron) and are rather sensitive to the dependence of the first-neighbor one-electron interaction with the interatomic distance. A large number of results on polyacetylene and polyheterocycles shows that there exists a simple law between the polarizability and the electronic gap, independently of the type of the monomeric unit. But this relation shows a deviation from a simple proportionality behavior, as soon as α reaches large values (as for example in polymers with defects).

Ground-State Properties of the One-Dimensional Isotropic Spin-1/2 Heisenberg Antiferromagnet with Competing Interactions

The ground-state properties of the one-dimensional isotropic spin-1/2 Heisenberg antiferromagnet with antiferromagnetic first- and second-neighbor exchange interactions are discussed. The ground-state energy, the singlet-triplet energy gap, the Néel correlation function, the dimer correlation function, and the magnetization are calculated exactly for finite-size systems up to 20 spins. By extrapolating these results, the values of the above quantities at the infinite-size limit are estimated. In particular, it is found that the limiting ground state is in the gapless or finite-gap phase depending on whether 0≦ j ≦ j c or j > j c , where j is the ratio of the second- to the first-neighbor interaction constant and j c =0.30±0.01. Dimer long-range order does exist in the finite-gap phase and it does not in the gapless phase, while no Néel long-range order exists in both phases.

Dielectric properties of dilute bcc antiferroelectric systems.

A model is presented for the calculation of the static dielectric properties of pure and dipole-dilute bcc antiferroelectric systems. The real systems display long-range dipolar and elastic interactions, which are simulated in this paper by an effective Hamiltonian with first- and second-neighbor interactions only. The first-neighbor interaction is taken to be antiferroelectric but the second neighbors, although ferroelectrically ordered at T=0 K for the pure systems, are allowed to interact via (i) a ferroelectric or (ii) a weak antiferroelectric coupling. The cluster-variation method is used to treat this model. The results show that the dielectric properties are qualitatively different in cases (i) and (ii). We conjecture that in orthorhombic KCN the effective second-neighbor interaction is antiferroelectric. The model is also of interest for other antiferroelectric and antiferromagnetic systems.