The fluid-solid transition of Dzugutov's potential

We have studied fluid-solid phase transformations of materials interacting via the Dzugutov potential (Phys. Rev. A 46, R2984 (1992)). We present evidence from molecular dynamics simulations that this interaction does not exhibit a liquid phase. If a mixed potential (r) is formed by a linear superposition of and the Lennard-Jones potential , then the liquid phase disappears at a fraction of less than 60% . Received 15 June 1998 and Received in final form 8 July 1999     

Quantum fluid-solid transition in a simple variational approach

A determinant (permanent) of plane waves for N fermions (bosons) in their lowest-energy state, and a determinant (permanent) of spatially-localized, nonoverlapping, single-particle functions are used to determine conditions on the short-ranged, square-well repulsive plus Yukawa attractive, two-body potential for which the spatially homogeneous or periodic particle-density states are energetically preferred. A considerable region in the coupling parameter-density plane is found where “crystalline” solutions are preferred. In particular, for purely repulsive forces, the low-density region for which the “fluid” solution is lowest shrinks to zero in the limit of infinitely repulsive cores, but faster for bosons than fermions. Inclusion of attractive forces is seen not to alter qualitatively the main results.     

Thermal conductivity in a rigidity transition

The thermal conductivity (κ(T)) in a lattice is studied as a function of rigidity by using the Kubo-Greenwood formula. The rigidity is modulated by changing the second neighbour interactions. The results show that κ(T) is strongly determined by the rigid character of the network through the low frequency vibrational modes. The transition from an isostatic to overconstrained lattices is thus reflected in the behavior of κ(T).     

Spectral rigidity and eigenfunction correlations at the Anderson transition

The statistics of energy levels for a disordered conductor are considered in the critical energy window near the mobility edge. It is shown that, if the critical wave functions are multifractal, the one-dimensional gas of levels on the energy axis is compressible, in the sense that the variance of the level number in an interval is 〈 (δN)²〉∼χ〈N〉 for 〈N〉≫1. The compressibility, χ=η/2d, is given exactly in terms of the multifractal exponent η =d−D ₂ at the mobility edge in a d-dimensional system. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 355–360 (10 September 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Scaling law for the fluid-solid phase transition in Yukawa systems (dusty plasmas)

Yukawa systems serve as models for plasmas and colloidal suspensions of charged particles. The state of these systems is determined by two dimensionless parameters: k = a/λ _D , which is the ratio of the mean interparticle distance to the Debye length λ _D , and Γ = Z _d ² e ²/aT _d , which is the ratio of the Coulomb potential energy to the particle temperature T _d (Z _d is the charge of each particle). We propose an empirical scaling law for the critical coupling parameter Γ _c needed for crystallization in Yukawa systems. The dependence of Γ _c on k is in good agreement with recent molecular dynamics simulations.     

Giant photoplastic effect in vitreous semiconductors near the rigidity percolation transition

The negative giant photoplastic effect (giant photosoftening) has been experimentally observed in the As-Se system when films obtained by thermal evaporation of As₂₀Se₈₀ chalcogenide glass are irradiated by light from the region of the fundamental absorption edge. Correlation has been found between the photoplastic effect and rigidity percolation transition in the As-Se chalcogenide glass matrix. Such a correlation is not revealed when light irradiation changes the optical properties of these glass films. It has been shown that a nonlinear (non-Hookian) mechanism of the formation of the strain response is realized in the films subjected to the combined action of light and external mechanical loading.     

Lyapunov instability, local curvature, and the fluid-solid phase transition in two-dimensional particle systems

We study the relation between the Lyapunov spectrum and the multidimensional geometry of the potential energy surface in terms of the distribution of stable and unstable modes for different models. For this purpose we determined Lyapunov exponents for the so-called correlated cell model and its smooth generalization as a function of the density for various energies. In the smooth case averaged structural quantities, such as the fraction of unstable modes, the Gaussian curvature, and the Riemannian curvature were computed and compared to the mechanical instability of the system in the sense of Lyapunov. A similar analysis was also carried out for 36-disk systems representing various fluid and solid states. In all studied cases the most-positive Lyapunov exponent exhibits a maximum at the phase transition in agreement with results for the fluid-solid transition in many-particle systems.     

Emergence of long-range correlations and rigidity at the dynamic glass transition

At the so-called dynamic glass transition predicted by the mean-field replica approach equilibrium liquid's translational symmetry is spontaneously broken, albeit at the microscopic level. We show that this fact implies the emergence of Goldstone modes and long-range density correlations. We derive and evaluate a new statistical mechanical expression for the glass shear modulus.     

Light-induced giant softening of network glasses observed near the mean-field rigidity transition

The longitudinal acoustic (LA) mode of bulk GexSe1-x glasses is examined in Brillouin scattering (BS) over the 0.15相似文献   

Crystal bridge formation marks the transition to rigidity in a thin lubrication film

We report that the rheological transition in a thin lubrication film of dodecane from bulk to high viscosity states as the thickness is decreased is the result of a novel structural transition. Using nonequilibrium molecular dynamics simulations we find that the initial increase in viscosity as the film thins is due to the formation of isolated crystalline bridges between the surfaces. As the thickness decreases further, these bridges increase in number and organize themselves into a tetratic order in the plane of the surface. We show that this ordered state melts at a temperature of 350 K.     

Role of hybridization in phase transition in the Falicov-Kimball model

Extended Falicov-Kimball model has been considered for samarium-chalcogenides where, (a) f-f interactions are considered to be quite large, (b) periodicity of the system has been taken into account, (c) f-d interactions are considered within mean field approximation and (d) the unperturbed conduction bandwidth is taken to be non-zero. We observe both continuous as well as discontinuous transitions and hence conclude that “extended Falicov-Kimball model” is a suitable model which can describe both a first order transition and a suitable intermediate valence phase in Sm-chalcogenides.     

Role of multistability in the transition to chaotic phase synchronization

In this paper we describe the transition to phase synchronization for systems of coupled nonlinear oscillators that individually follow the Feigenbaum route to chaos. A nested structure of phase synchronized regions of different attractor families is observed. With this structure, the transition to nonsynchronous behavior is determined by the loss of stability for the most stable synchronous mode. It is shown that the appearance of hyperchaos and the transition from lag synchronization to phase synchronization are related to the merging of chaotic attractors from different families. Numerical examples using Rossler systems and model maps are given. (c) 1999 American Institute of Physics.     

Role of material amorphicity in laser-induced phase transition

The crystallization patterns induced by nano- and picosecond laser pulses within an amorphous matrix, with various degrees of relaxation, present morphological instabilities. We show by TEM observations that the final crystalline structures of the relaxed amorphous state, after nanosecond laser excitation, and the “as-deposited” amorphous state after picosecond excitation, present similar morphology. Structurally, metastable crystalline states have been formed under laser irradiation. A probable process for these instabilities is related to competition between the light-induced electronic excitation and thermal processes during the nucleation stage.     

Role of the gas-liquid phase transition in the theory of nuclear matter

A sufficient condition for the two-nucleon interaction to produce a gaseous instability in the form of the appearance of inhomogeneous-spatial-density single-particle states of lower energy than the (homogeneous) plane-wave states is found to be simply that it gives binding in first order. The critical density at which the instability occurs thus signals the unambiguous breakdown of a plane-wave-based Hartree-Fock perturbation expansion for the ground state properties. Several examples are analysed.     

Role of protein-water hydrogen bond dynamics in the protein dynamical transition

The role of water in protein dynamics has been investigated using molecular dynamics simulations of crystals and a dehydrated powder. On the 100 ps time scale, the anharmonic and diffusive motions involved in the protein structural relaxation are correlated with the protein-water hydrogen bond dynamics. The complete structural relaxation of the protein requires relaxation of the hydrogen bond network via solvent translational displacement. Inhibiting the solvent translational mobility, and therefore the protein-water hydrogen bond dynamics, has an effect on the protein relaxation similar to dehydration.