Phase diagram of a one-dimensional model with nonconvex interactions,using the method of effective potentials

The ground states of a one-dimensional system of the Frenkel-Kontorova type, but involving piecewise parabolic potentials, including a nonconvex interatomic interaction, have been studied numerically using the method of effective potentials. Part of the phase diagram is identical to one studied earlier for a convex interaction, and part of it exhibits some new phases, first-order phase transitions, multicritical points, and an accumulation point of multicritical points, all associated with the nonconvex interaction.     

On the validity of the triple-dipole interaction as a representation of non-additive intermolecular forces

A complete partial wave analysis of the non-expanded non-additive coulomb interaction energy for three non-degenerate S-state atoms is given through third-order in the interatomic potential energy function. Pseudo state techniques are used to evaluate various partial wave components of the non-expanded second and third-order non-additive interaction energies for various isosceles triangular configurations of three interacting ground-state hydrogen atoms. These second and third-order non-expanded coulomb results are used, in conjunction with Heitler-London results for the first-order non-additive energies for the quartet spin state of the H(1s)-H(1s)-H(1s) interaction, to discuss the relative importance of various parts of the non-additive energy as a function of the geometrical configuration of the atoms, and the validity of both the non-expanded triple-dipole energy and the expanded Axilrod-Teller-Muto triple-dipole result as a representation of non-additive coulomb energies. For example, in the non-bonded interaction of three S-state atoms it appears that representing the non-additive energy by the non-additive coulomb energy is not reliable until the interatomic separations are somewhat larger than R*, the interatomic distance associated with the van der Waals minimum in the corresponding non-bonded dimer interaction. Further, the use of the triple-dipole interaction energy, with or without charge overlap corrections, to represent the non-additive coulomb energy is of doubtful validity until the interatomic separations are considerably greater than R*.     

Quantum Teleportation and Resonance Information Transfer from One Atom to Another at Arbitrary Interatomic Distances

The feasibility of resonance transfer of quantum information from one double-level atom to another that is at an arbitrary distance from the former one has been proved. Symmetric and antisymmetric combinations of the wave functions of individual atoms are considered. When taking into account the interatomic dipole–dipole interaction, a certain energy corresponds to each wave function. A solution has been found to a system of equations for the amplitudes of the probability that a resonance photon will be absorbed by one of the system atoms, and it has been shown that the interaction of the system with actual photons has the result that the wave function of the final state of the system can be represented as a linear combination of the functions < 00|, < 0n|, and < n0| corresponding to the ground and excited states of individual atoms. The amplitude of the probability of each of these states depends on the interatomic distance and on the parameters of the action of actual photons on atoms. Three types of solution to the system of equations have been investigated for the resonance and nonresonance absorption of photons and different interatomic distances. It has been shown that when atoms are at an infinite distance from one another, so that there is no dipole–dipole interaction of atoms, quantum information can be transferred from one atom to another with a characteristic time considerably shorter than the time it takes for a photon to cover the interatomic distance. This effect is referred to as the effect of quantum teleportation in a system of resonance atoms.     

The sputtering properties of artificial polymorphic AB binary compound crystals

Molecular dynamics (MD) simulations of the sputtering of artificial 1:1 binary compound targets, AB, are reported. The simulations explore the sensitivity of monomer and dimer sputter yields to AB target structure and interatomic potentials. The targets have the sphalerite, wurtzite and sodium chloride lattice structures, and their atomic and material properties resemble those of ZnS polymorphs. Two different sets of interatomic potentials were used for the simulations. In the symmetric model, all bonding interactions are equivalent, while in the asymmetric model, the A-B interactions are strengthened at the expense of the A-A and B-B interactions. Both models predict similar material properties for a given target. No systematic variations of sputter yields for individual targets can be discerned between the predictions based on the symmetric and asymmetric interaction models. The relative sputter yields of monomer species A and B are independent of target structure when the A and B atoms occupy surface sites of equivalent symmetry. The relative yields of the AA and BB dimer species are similarly insensitive to the target structure, but target-dependent variations of the relative yields of AB dimers are observed. Sputtering properties other than relative yields (e.g. clustering range, depth of origin) do show structure-dependent variations. In agreement with previous MD studies of sputtering from metals, the nearest-neighbour contribution to AB clusters is found to be typically ∼50%, and may be as low as 30%.     

三体相互作用下Bessel型光晶格中物质波孤立子的稳定性研究

研究了两体和三体相互作用空间调制情形下Bessel型光晶格中准二维玻色-爱因斯坦凝聚体系中物质波孤立子的稳定性. 利用标准的变分法程序, 得出体系有效势能的表达式, 进而根据有效势能结构给出了体系的稳定性条件. 结果表明, 在有Bessel型光晶格和没有Bessel型光晶格的情况下, 体系均能形成稳定的孤立子解, 但是有晶格参与时, 体系有很大范围的稳定区间. 另外, 稳定性受两体相互作用和三体相互作用共同支配, 其中两体相互作用对体系的稳定性起主导作用, 三体相互作用和相互作用的空间调制只对稳定性起调节作用, 但是在特定情况下, 必须要有三体相互作用或者相互作用空间调制的参与才能形成稳定的孤立子解.     

三体相互作用下Bessel型光晶格中物质波孤立子的稳定性研究

研究了两体和三体相互作用空间调制情形下Bessel型光晶格中准二维玻色-爱因斯坦凝聚体系中物质波孤立子的稳定性.利用标准的变分法程序,得出体系有效势能的表达式,进而根据有效势能结构给出了体系的稳定性条件.结果表明,在有Bessel型光晶格和没有Bessel型光晶格的情况下,体系均能形成稳定的孤立子解,但是有晶格参与时,体系有很大范围的稳定区间.另外,稳定性受两体相互作用和三体相互作用共同支配,其中两体相互作用对体系的稳定性起主导作用,三体相互作用和相互作用的空间调制只对稳定性起调节作用,但是在特定情况下,必须要有三体相互作用或者相互作用空间调制的参与才能形成稳定的孤立子解.     

Monte Carlo simulation using the Fourier transform of the interatomic potential

When doing Monte Carlo simulations using continuous potentials, the evaluation of the configurational potential energy ink-space by Fourier transformation is shown to be a computationally attractive scheme for systems where the long-range interatomic interaction spans a dimension comparable to the size of the simulated system.     

Resonance Interaction Energy in κ-Minkowski Spacetime

If gravity is quantized, one of the consequences may be that the spacetime coordinates are quantized and become noncommutative. The κ-Minkowski spacetime is such kind of noncommutative spacetime. In this paper, the resonance interaction energy of a two-atom system coupled with a fluctuating vacuum scalar field in the κ-Minkowski spacetime is studied. It is found that the resonance interaction energy is dependent on the interatomic separation, the transition wavelength of the atoms, and the spacetime non-commutativity. When the interatomic separation is small compared with a characteristic length determined by the spacetime non-commutativity parameter and the transition wavelength, the resonance interaction energy is that in the Minkowski spacetime plus a correction due to the spacetime non-commutativity. When the interatomic separation is comparable to or larger than the characteristic length, the resonance interaction energy cannot be organized in the form of a Minkowski term plus a correction, which indicates that the long-range behavior of the vacuum in the κ-Minkowski spacetime is fundamentally different from that in the Minkowski spacetime.     

Influence of crystal dimensions on interatomic distances in dispersed carbon

The relationship between the interatomic distances and crystal dimensions in dispersed carbon is studied by x-ray structure analysis and by performing model calculations. It is established that the interatomic distances in dispersed carbon are determined by the dimensions of the crystals along the crystallographic a axis (L _a). Small crystal dimensions dictate smaller interatomic distances than in graphite; an increase in the crystal dimensions leads to a corresponding increase in this parameter. The interatomic distances in dispersed carbon depend on the degree in covalency of the bonding, which is a function of L _a. Fiz. Tverd. Tela (St. Petersburg) 41, 744–747 (April 1999)     

Development of a ReaxFF description for gold

Atomistic simulations of the chemistry of thiol-gold-systems have been restricted by the lack of interatomic interaction models for the involved elements. The ReaxFF framework already has potentials for hydrocarbons, making it an attractive basis for extending to the complete AuSCH-system. Here, an interatomic potential for gold, based on the ReaxFF framework, is presented and compared to existing gold potentials available in the literature. Electronic supplementary material  Supplementary Online Material     

S-d Exchange Interaction and the Invar Anomaly of Thermal Expansion of Weak Band Magnets (on the Example of Fe1–x Co x Si Solid Solutions)

In the present paper, the temperature dependence of the linear thermal expansion coefficient (LTEC) of weak band magnets is studied both theoretically and experimentally on the example of Fe_1–x Co _x Si solid solutions. The contributions of electron and magnetic components are also analyzed. It is demonstrated that the experimental data obtained cannot be explained within the framework of the well-known single-particle models. A theoretical approach describing contributions of electrons and fluctuations to the LTEC of weak band magnets is developed based on the spd-model which, in addition to the interatomic exchange interaction of d-electrons, considers the spd-interaction resulting in a noticeable shift of the chemical electron potential along the energy axis. It is demonstrated that the exchange interaction of magnetic moments of s,p- and d-electrons plays the important role in the formation of the Invar LTEC anomaly in Fe_1–x Co _x Si solid solutions.     

Quasihard-sphere model in simulation of the processes of particle scattering

A model of interatomic potentials of interaction is suggested for static simulation of the processes of elastic scattering of atomic particles by atoms of gas, plasma, and solid. In the developed model, the atomic particle radii, whose magnitude depends on the energy of their relative motion, are internal parameters. The suggested quasihard-sphere model enables one to simulate elastic processes of scattering of atomic particles, using different interatomic potentials of interaction with relatively high rates of statistical simulation characteristic of simulation within the hard-sphere model. The Born-Mayer potential is selected as the interatomic potential of interaction and modified for a wide class of partners in atomic collisions. It is demonstrated that the suggested mathematical model of quasihard spheres describes fairly correctly the processes of elastic scattering of atoms in a gas medium and of displaced atoms in a solid with an almost constant rate of static simulation.     

Molecular dynamics of liquid lead near its melting point

The molecular dynamics of liquid lead is simulated at T = 613 K using the following three models of an interparticle interaction potential: the Dzugutov pair potential and two multiparticle potentials (the “glue” potential and the Gupta potential). One of the purposes of this work is to determine the optimal model potential of the interatomic interaction in liquid lead. The calculated structural static and dynamic characteristics are compared with the experimental data on X-ray and neutron scattering. On the whole, all three model potentials adequately reproduce the experimental data. The calculations using the Dzugutov pair potential are found to reproduce the structural properties and dynamics of liquid lead on the nanoscale best of all. The role of a multiparticle contribution to the glue and Gupta potentials is studied, and its effect on the dynamic properties of liquid lead in nanoregions is revealed. In particular, the neglect of this contribution is shown to noticeably decrease the acoustic-mode frequency.     

Controlling multiparticle correlations with a strong laser field

The collective interaction via a surrounding thermalized electromagnetic reservoir of a two-level multiatom sample with an external applied strong coherent field is investigated. In a small sample following Dicke’s model, even at the exact resonances, very strong pumping leads to a complete transfer of the population into a particular dressed-state. This way very large Rabi frequencies are shown to modify and control the interatomic correlations in a system of spatially separated atoms of few wavelengths extend.     

Models for Gapped Boundaries and Domain Walls

We define a class of lattice models for two-dimensional topological phases with boundary such that both the bulk and the boundary excitations are gapped. The bulk part is constructed using a unitary tensor category C{\mathcal C} as in the Levin-Wen model, whereas the boundary is associated with a module category over C{\mathcal C} . We also consider domain walls (or defect lines) between different bulk phases. A domain wall is transparent to bulk excitations if the corresponding unitary tensor categories are Morita equivalent. Defects of higher codimension will also be studied. In summary, we give a dictionary between physical ingredients of lattice models and tensor-categorical notions.     

Role of thermal vibrations in alloy phase transitions

We resolve the fundamental contradiction that has existed from the earliest studies on order–disorder transitions between theoretical models that ignore the effect of thermal vibrations on the chemical interaction parameter, J(0), and the analysis of diffraction data that always incorporates the role of vibrations. New analysis of diffraction data shows that the temperature dependence of the order parameter, the central feature of order–disorder transitions, predicted by existing models is scientifically invalid. All models are constrained by the diffraction data to represent the interaction parameter as J(T) and the ordering energy as temperature dependent. The discrepancy between the experimental and theoretical ordering energies in Ni₃V and Pd₃V is direct evidence of their temperature dependence. Thermal vibrations influence order–disorder transitions through both the configurational and vibrational terms and not just the vibrational terms as hitherto believed. A modified Bragg–Williams model is proposed, which is the simplest model whose predicted order parameter can be compared with experiments.     

Interatomic potential effects on dynamical heterogeneities in liquid SiO2

Dynamical heterogeneities (DH) in low density liquid SiO₂ have been investigated by molecular dynamics (MD) method. Simulations were done in the basic cube under periodic boundary conditions containing 3000 particles with the pair interatomic potentials, which have a weak electrostatic interaction and a Morse type short range interaction (PMSI). We have evaluated the non-Gaussian parameter for the self part of the van Hove correlation function and we found a clear evidence of the existence of DH in low density liquid SiO₂. Moreover, the atomic displacement distribution (ADD) in a model has been obtained and it deviates from a Gaussian form. The results have been compared with those obtained in another liquid SiO₂ system with the Born-Mayer interatomic potentials (BMP) in order to observe the interatomic potential effects on the DH in the system and indeed, the effects are strong. Calculations showed that particles of extremely low or fast mobility have a tendency to form a cluster and mean cluster size of most mobile and immobile particles in PMSI models increases with decreasing temperature. In contrast, no systematic changes have been obtained for the most mobile and immobile particles in BMP models. Calculations show that there is no relation between local particle environment and particle mobility in the system.     

Large Deviation Techniques Applied to Systems with Long-Range Interactions

We discuss a method to solve models with long-range interactions in the microcanonical and canonical ensemble. The method closely follows the one introduced by R.S. Ellis, Physica D 133:106 (1999), which uses large deviation techniques. We show how it can be adapted to obtain the solution of a large class of simple models, which can show ensemble inequivalence. The model Hamiltonian can have both discrete (Ising, Potts) and continuous (HMF, Free Electron Laser) state variables. This latter extension gives access to the comparison with dynamics and to the study of non-equilibrium effects. We treat both infinite range and slowly decreasing interactions and, in particular, we present the solution of the α-Ising model in one-dimension with 0 ⩽ α < 1.     

Interatomic interaction potentials and their application to the description of particle scattering by a surface

The data on interatomic interaction potentials obtained from experiments are compared with the well-known theoretical models of potentials. A new analytical form of a potential that provides the best fit for experiments is proposed. The accuracy of its application is estimated as a function of the internuclear distance under consideration. Individual potentials for systems consisting of inert gases are discussed, and an algorithm for constructing potentials is proposed for cases not yet studied.