Hurst's empirical law in the probability of atomic distribution in liquids

The rescaled range analysis was used to examine the pair distribution function of liquids. The global statistical dependence existed in the distribution of atoms in liquids. The probability of finding a particle at a distance r from a reference particle was subject to fractional Brownian motion. More importantly, the tendency of the Hurst exponent was away from the high rate when the change of liquid structure took place. This phenomenon showed that the liquid structural change was attributed to the variation of atomic distribution and the jump of the Hurst exponent was the indicator of the change from one phase to another in liquids.     

Molecular Dynamical Simulation of Water/Ice Phase Transitions within Carbon Nanotubes under Various Pressures

A molecular dynamics simulation is performed for water confined within carbon nanotubes with diameters 11.00 A and 12.38A. Under pressures from 0.1 MPa to 500MPa the simulations are carried out by cooling from 300 K to 240K. Water molecules tend to transform from disordered to ordered with different configurations （square, pentagonal, hexagonal and hexagonal plus a chain）. It is concluded that denser structures may appear under high pressures.     

Glass Transition Temperature of Water： from Simulations of Diffusion and Excess Entropy

We report a computer simulation study of the glass transition of water with SP2 potential. The temperature dependences of the diffusion coefficient and the excess entropy on cooling process are calculated. It is found that both the diffusion coefficient and the excess entropy show a break point at 160K. Our results support the viewpoint that the glass transition temperature is 160K. According to the calculated viscosity, we obtain a fragility index of water to be 326, which is much larger than the value accepted before.     

Insulator-conductor transition in liquid aluminium trichloride

We report molecular-dynamics simulations of ionic structure and diffusion in a pseudoclassical model of AlCl₃ over a wide region of the pressure-temperature (p,T) plane. The model melts from a layer crystal into a molecular liquid at low (p,T) and into a dissociated ionic liquid at high (p,T), in accord with x-ray diffraction studies of the AlCl₃ material. We show that pressure drives a broad liquid-liquid transition from a molecular insulator to an ionic conductor and trace the transition line in the (p,T) plane. This line has a negative dp/dT slope and appears to branch out from an anomaly in the melting curve.     

Covalent-to-ionic transition in liquid zinc dichloride

We report molecular-dynamics simulations of self-diffusion and structure in a pseudoclassical model of liquid and crystalline ZnCl₂ over a wide region of the pressure-temperature plane. The model parameters are adjusted to reproduce a liquid structure of corner-sharing ZnCl₄ tetrahedra at the standard freezing point and the measured diffusion coefficients as functions of temperature on the sfp isobar. We find that compression first weakens the intermediate-range order of the melt near freezing into a fourfold-coordinated crystal structure, and then drives at higher temperatures a novel liquid-liquid transition consisting of two broad steps: (i) a transition in which the Zn atoms start to leave their tetrahedral cages, followed by (ii) a structural transition from a covalent network of Cl atoms to a dissociated ionic liquid which then freezes into a sixfold-coordinated crystal. Good agreement is found with data from X-ray diffraction experiments under pressure.     

Au doped Sb3Te phase-change material for C-RAM device

Au doped Sb₃Te phase-change films have been investigated by means of in situ temperature-dependent resistance measurement. Crystallization temperature of 2 at.% Au doped Sb₃Te has been enhanced to 161 °C, which leads to a better data retention. The physical stability of the film has been improved evidently after adding Au as well. Resistance contrast has been improved to 1.1 × 10⁴, one order of magnitude higher than that of pure Sb₃Te. X-ray diffraction patterns indicate the polycrystalline Au-SbTe series have hexagonal structure, similar with pure Sb₃Te alloy, when Au doping dose is less than 9 at.%.     

Ge1Sb2Te4 Based Chalcogenide Random Access Memory Array Fabricated by 0.18-μm CMOS Technology

Ge1Sb2Te4-based chalcogenide random access memory array, with a tungsten heating electrode of 260hm in diameter, is fabricated by 0.18-μm CMOS technology. Electrical performance of the device, as web as physical and electrical properties of GelSb2 Te4 thin film, is characterized. SET and RESET programming currents are 1.6 and 4.1 mA, respectively, when pulse width is 100 ns. Both the values are larger than those of the Ge2Sb2 Tesbased ones with the same structure and contact size. Endurance up to 106 cycles with a resistance ratio of about 100 has been achieved.     

Formation of amorphous films by solid-state reaction in an immiscible Y-W system

Received: 26 November 1996/Accepted: 7 February 1997     

Molecular Dynamics Study of Stability of Solid Solutions and Amorphous Phase in the Cu-Al System

The relative stability of fee and bcc solid solutions and amorphous phase with different compositions in the Cu-Al system is studied by molecular dynamics simulations with n-body potentials. For CU1-xAlx alloys, the calculations show that the fee solid solution has the lowest energies in the composition region with x 〈 0.32 or x 〉 0.72, while the bcc solid solution has the lowest energies in the central composition range, in agreement with the ball-milling experiments that a single bcc solid solution with 0.30 〈 x 〈 0.70 is obtained. The evolution of structures in solid solutions and amorphous phase is studied by the coordination number （CN） and bond-length analysis so as to unveil the underlying physics. It is found that the energy sequence among three phases is determined by the competition in energy change originating from the bond length and CNs （or the number of bonds）.     

Spatial arrangements of particles with different mobility tendencies in a model glass-former

The use of the isoconfigurational method has enabled one to determine the existence of particles with high and low dynamic propensity (tendency to be mobile) and particles with preferred directionality for motion (directional particles) in supercooled liquids. On the other hand, dynamical studies have shown that the relaxation of such systems evolves by means of rapid crossings between metabasins of the potential energy surface (a metabasin being a group of mutually similar, closely related structures which differ markedly from the ones belonging to other metabasins), as collectively relaxing units (d-clusters) take place. Here we determine the spatial arrangements of such particles in a model three dimensional glass-forming system. We show that both the highest and the lowest propensity particles form compact clusters, which are separated from each other by the high directionality particles. The particles of this interfacial region seem to behave as to help make room for the enhanced (expansion) movement of the high propensity cluster and to keep the local density constant. Finally, we also find that only the high propensity particles (but not the directional ones) exhibit a great tendency to take part in d-cluster events.     

A core-softened fluid model in disordered porous media. Grand canonical Monte Carlo simulation and integral equations

We have studied the microscopic structure and thermodynamic properties of a core-softened fluid model in disordered matrices of Lennard-Jones particles by using grand canonical Monte Carlo simulation. The dependence of density on the applied chemical potential (adsorption isotherms), pair distribution functions, as well as the heat capacity in different matrices are discussed. The microscopic structure of the model in matrices changes with density similar to the bulk model. Thus one should expect that the structural anomaly persists at least in dilute matrices. The region of densities for the heat capacity anomaly shrinks with increasing matrix density. This behavior is also observed for the diffusion coefficient on density from independent molecular dynamics simulation. Theoretical results for the model have been obtained by using replica Ornstein-Zernike integral equations with hypernetted chain closure. Predictions of the theory generally are in good agreement with simulation data, except for the heat capacity on fluid density. However, possible anomalies of thermodynamic properties for the model in disordered matrices are not captured adequately by the present theory. It seems necessary to develop and apply more elaborated, thermodynamically self-consistent closures to capture these features.     

Molecular Dynamics Simulation of Water Confined in Carbon Nanotubes

Molecular dynamics simulations are performed for water confined in carbon nanotubes with various diameters （11.0-13.8 A ）. The simulations under an isobaric pressure （one atmosphere） by lowering temperatures from 300 K to 190K are carried out. Water molecules within variously sized tubes tend to transform from disorder to order with different configurations （four-water-molecule ring, six-water-molecule ring and seven-water-molecule ring） at phase transition temperatures, which may be lowered by the increasing tube radius. It is also found that the configurations of water in （10, 10） tube are not unique （seven-molecule ring and seven-molecule ring plus water chain）.     

Long-Term Thermal Stability of Binary Cu50.3Zr49.7 Bulk Metallic Glass

We investigate the kinetics and thermal stability of a simple Cu50.3Zr49.7 binary bulk metallic glass （BMG）. The long-term thermal stability of CU50.3Zr49.7 BMG is evaluated by a newly developed method from an extension of Vogel- Fulcher-Tammann analysis. The method has been proven to be valid in CU50.3Zr49.7 or even other BMGs.     

Growth exponent in the Domany-Kinzel cellular automaton

Dynamic heterogeneities, i.e. the presence of molecules with different mobilities, have been established as one of the key features of the physics of supercooled liquids. Here we study in detail how the mobility of an individual molecule fluctuates with time. Our analysis is based on a time series of molecular dynamics simulations for a low molecular weight glass-former, propylene carbonate. We find that the variation of mobility with time of initially slow molecules significantly differs from that of initially fast molecules. We explicitly show the relation to the rate memory parameter which recently has been introduced to quantify the mobility fluctuations as observed via multidimensional NMR experiments. In this way qualitative agreement between simulation and experiment can be established although the time scales of simulation and NMR experiment differ by many orders of magnitude. Received 10 April 2000 and Received in final form 21 September 2000     

Single-chain dynamics of linear polyethylene liquids under shear flow

Molecular dynamics simulations of linear C₇₈H₁₅₈ were conducted to investigate the dynamics of individual chains under shear. The distribution of the end-to-end vector exhibited Gaussian behavior at low shear rates; however, it displayed a bimodal form at high shear rates as rotational motion of the individual chains effectively lowered the vector's magnitude. Correlations between the components of the end-to-end vector revealed multiple time scales associated with the fluid response: the Rouse time, and several that were associated with the deformation and rotational dynamics of the fluid.     

Formation of NiZr2 Binary Metallic Glass： Experimental and Molecular Dynamics Analyses

The local atomic structure of an amorphous NiZr2 alloy is identified by using x-ray diffraction, transmission electron microscopy, and differential scanning calorimeter. Based on the experimental results, molecular dynamics simulation is performed to investigate the glass formation of liquid NiZr2 alloy. Some relevant features of the pair correlation functions are in good agreement with those obtained by experiment. The pair analysis parameters are calculated, suggesting that there exist icosahedral ordering, four-fold symmetrical bipyramid and triangular- faced polyhedral units in the amorphous NiZr2 structure. The result is beneficial to open avenues toward the understanding of fundamental theoretical problems of glass formation of simple binary alloys.     

Structural phase transformation of GaN under high-pressure: an exact exchange study

The phase transformation of GaN under high pressure is theoretically studied in the KS-DFT framework using the EXX method. Both KLI and LDA pseudopotentials were tried. The LDA-PP result for the transition pressure is 41.7 GPa while that of the KLI-PP is 41.5 GPa. Both results are in a very good agreement with the latest experimental value of 42 GPa. The effect of the nonlinear core correction is found to be small but not negligible.     

Elastic Analysis of Physisorption-Induced Substrate Deformation

Physisorption may cause a dimple on a deformable solid surface due to adsorbat-substrate interaction. The interactive force between the adsorbate and the crystal atoms depends on their distances, which may change with substrate deformation. This feature of displacement-dependence indicates that the equilibrium problem is a force-deformation coupled nonlinear procedure. In the present study, a continuum mechanics model, in which the force is considered as a function of the displacement field of the medium, is presented to calculate the physisorption-induced deformation in a semi-infinite elastic medium. It is found that the nonlinear effect due to force-deformation coupling should be taken in consideration in the adsorbate-substrate interaction analysis.     

Structural study on the crystallization behavior of Sb3Te2 alloy for phase change memory

The atomic crystal structure of the Sb₃Te₂ binary alloy has been investigated with high‐resolution transmission electron microscopy (HR‐TEM) and fast Fourier transform patterns. As a result, there is inconsistency between the previous theoretical model and the experimental result. But, from the calculations of lattice parameters and the number of layers in the unit cell, it is found that the Sb₃Te₂ alloy can be crystallized into the Sb₂Te structure with P m1 space group and the difference between stacking sequences of the Sb₃Te₂ and the Sb₂Te structures has been discussed with the proposed atomic arrangement model of unit cells. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evolution of prisoner's dilemma strategies on scale-free networks

The evolution of strategies in the iterated prisoner's dilemma on scale-free networks is investigated. It is found that the smaller the average degree is, the easier it is to promote cooperation by natural selection. Cooperation on scale-free networks built upon big clustering coefficients is enhanced and maintained at a high level. The introduction of punishment strategy for unsatisfied agents also increases cooperation and improves its persistence on scale-free networks.