Interplay between gas adsorption and dislocation structure on a metal surface

The influence of oxygen and sulfur on the dislocation patterns of the strained two monolayer Cu film on Ru was observed by scanning tunneling microscopy. Both oxygen and sulfur adsorption lead to the formation of vacancies that aggregate over existing dislocations in the film, thereby modifying the dislocation structure. With increasing adsorbate coverage the overall dislocation structure and pattern are transformed. The atomic mechanisms and general nature of this transformation can be explained in terms of generic dislocation reactions. This interpretation is also supported by atomistic simulations.     

Structure and diffusion in aluminium and gallium trihalide melts from simulations based on intramolecular force laws

Diffraction studies of the liquid structure of AlCl₃, AlBr₃, GaBr₃ and GaI₃ close to their respective freezing points have revealed fourfold coordination of the trivalent metal ions, consistent with dimeric M₂X₆ molecules being the dominant species. We evaluate the species-resolved pair distribution functions and liquid structure factors in all these melts by carrying out classical molecular-dynamics simulations, based on polarizable-halogen force laws that were determined on isolated molecular monomers and dimers in the gaseous phase. We also report results for mean-square displacements and diffusion coefficients of the two species in each melt. The model reproduces the main features of the total neutron-diffraction structure factors, showing peaks due to intermediate-range order and to charge and density short-range order, and accounts for the experimental data at a good quantitative level. Direct simulation of the pair distribution functions yields agreement with the diffraction data on metal–halogen and halogen–halogen bond lengths in the melt and on the stability of the first-neighbour shell of the metal ions. We examine the temperature dependence of the liquid structure in our models for GaBr₃ and AlCl₃ and emphasize the structural role of van der Waals interactions between the halogens.     

聚氨酯结构与径向分布的分子动力学模拟

采用分子动力学方法计算得到DHI-乙烯醇聚合体系统的结构和径向分布函数。讨论了系统结构和径向分布函数与温度和压力之间的关系。结果表明粘合系统的空间分布一般地随着温度和压力的增加而收窄,对增加聚氨酯系统的粘合性具有积极的意义。     

聚氨酯结构与径向分布的分子动力学模拟

采用分子动力学方法计算得到DHI-乙烯醇聚合体系统的结构和径向分布函数.讨论了系统结构和径向分布函数与温度和压力之间的关系.结果表明粘合系统的空间分布一般地随着温度和压力的增加而收窄,对增加聚氨酯系统的粘合性具有积极的意义.     

岩盐结构氧化锌物态方程的分子动力学模拟

利用分子动力学方法和有效经验对势模型对ZnO岩盐结构高温高压下的物态方程进行了研究， 发现分子动力学方法得到的ZnO岩盐结构的摩尔体积(300?1273 K，3.2?10.4 GPa)和实验结果吻合；另外，基于经验势模型的可靠性预测了1373?2273 K和0? 50 GPa的ZnO岩盐结构的P-V -T关系，并利用相应的热力学公式拟合得到了ZnO岩盐结构常态下的线性热膨胀系数、等温体模量及其对压力的一阶导数等重要的热力学参量．     

Ab initio study of the structure and dynamical properties of crystalline ice

We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase, in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3× 1× 1 supercell using the direct method. So far, due to the direct method used in this calculation, the phonon spectra are obtained without taking into account the effect of polarization arising from dipole–dipole interactions of water molecules, which is expected to yield the splitting of longitudinal and transverse optic modes at the Γ point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode are in reasonable agreement with the neutron scattering data. Analysis of the vibrational density of states shows the existence of a boson peak at low energy of the translational region, a characteristic common to amorphous systems.     

AlH分子结构与分析势能函数

本文运用群论及原子分子反应静力学方法,推导了 AlH分子的基态(X1Σ+)、第一激发态(A1Π)及第三激发态(C1S+)的电子态及相应的离解极限.并使用SAC/SAC-CI方法,采用D95 (d)、6-311g(d)和cc-PVTZ等基组对AlH分子的基态(X1Σ+)、第一激发态(A1Π)和第三激发态(C1S+)的平衡结构和谐振频率进行了几何优化计算.通过对三个基组的计算结果与实验结果的比较,得到cc-PVTZ基组是三个基组中最优基组的结论.使用cc-PVTZ基组,对AlH 分子的基态(X1Σ+)、第一激发态(A1Π)和第三激发态(C1S+)进行了单点能扫描计算,并给出了AlH的基态(X1Σ+)、第一激发态(A1Π) 和第三激发态(C1S+)的Murrell-Sorbie函数形式的电子态的完整势能函数,进而得到了AlH分子第一激发态(A1Π)的激发能较小的结论.     

Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min^–1) is studied by optical emission spectroscopy of O(⁵P) (line 777.4 nm) and of the atmospheric system of O₂(head‐line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(⁵P) and O₂(b). The concentration of the O(⁵P) atoms is in the range 108–109 cm^–3 and the concentration of the O₂(b) molecules is in the range 10¹⁴ – 2 × 10¹⁴ cm^–3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V‐V and V‐T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e‐e collisions. V‐V and V‐T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O^– and O₂^–, fundamental electronic neutral species O(³P), O₂, O₂(X,v), O₃ and excited neutral species O₂(a), O₂(b), O₂(A), O(¹D), O(¹S), O(⁵P), O(4d ⁵D^o), O(5s ⁵S^o), O(3d ⁵D^o) and O(4s ⁵S^o)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: – heterogeneous deactivation coefficient for O₂(b) γ = 2.6 × 10^–2; – rate constant of reaction [O(¹D) + O(³P) → 2 O(³P)] k₃₄ = 1.4 × 10^–11 cm³.s^–1; – electron concentration in the range 10¹⁰ – 10¹¹ cm^–3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10^–3 – 0.2 × 10^–3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O₂]initial) is about 33–50%. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

BCC Fe surface and cluster magnetism using a magnetic potential

A semi-empirical potential for ferromagnetic bcc iron that also models the co-linear magnetic moment of each atom, has been applied to clusters and surfaces. Surface energies of low index facets, surface relaxation and magnetic moment are calculated and compared to various other empirical potentials, recent density functional theory (DFT) results and experimental data. Quantitatively the resulting surface magnetic moments enhancements are underestimated, however qualitatively the general behavior of the magnetic moment as a function of surface or cluster layer is comparable to that predicted by DFT calculations.     

Electrons in a lattice with an incommensurate potential

A system of fermions on a one-dimensional lattice, subject to a weak periodic potential whose period is incommensurate with the lattice spacing and satisfies a Diophantine condition, is studied. The Schwinger functions are obtained, and their asymptotic decay for large distances is exhibited for values of the Fermi momentum which are multiples of the potential period     

Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium

Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.     

Atomic-scale simulation of nano-grains:structure and diffusion properties

Nanograins are characterized by a typical grain size from lto 100 nm.Mclecular dynamics aimubations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm.We study the influence of grain size on structure and diffusion properties of the nanograins.The results reveal that as the grain size is reduced,the fraction of grain surface increases significantly,and the surface width is approximately constant；the diffusicn coefficlent is increased sharply,and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10nm.     

Cu-Co双金属团簇结构演化及其性质的分子动力学模拟

采用分子动力学结合嵌入原子方法对比研究了Co分布于Cu-Co团簇不同层的结构和性质.研究表明:Co原子分层掺杂可对团簇的结构转变点和熔点进行诱导控制;分层掺杂的Cu-Co团簇第一相变是一种扩散度较小的由立方八面体转变为二十面体的相变;Co原子易于向低能态团簇的亚表层(111)面偏析,从而诱导团簇结构紊乱,造成其熔点差异.     

Cu-Co双金属团簇结构演化及其性质的分子动力学模拟

采用分子动力学结合嵌入原子方法对比研究了Co分布于Cu-Co团簇不同层的结构和性质. 研究表明：Co原子分层掺杂可对团簇的结构转变点和熔点进行诱导控制;分层掺杂的Cu-Co团簇第一相变是一种扩散度较小的由立方八面体转变为二十面体的相变;Co原子易于向低能态团簇的亚表层（111）面偏析, 从而诱导团簇结构紊乱, 造成其熔点差异.     

Interplay between social debate and propaganda in an opinion formation model

We introduce a simple model of opinion dynamics in which a two-state agent modified Sznajd model evolves due to the simultaneous action of stochastic driving and a periodic signal. The stochastic effect mimics a social temperature, so the agents may adopt decisions in support for or against some opinion or position, according to a modified Sznajd rule with a varying probability. The external force represents a simplified picture by which society feels the influence of the external effects of propaganda. By means of Monte Carlo simulations we have shown the dynamical interplay between the social condition or mood and the external influence, finding a stochastic resonance-like phenomenon when we depict the noise-to-signal ratio as a function of the social temperature. In addition, we have also studied the effects of the system size and the external signal strength on the opinion formation dynamics.     

A relation between structure and pair potential for liquid metals

We emphasize the importance of considering the relationship between the structure of a liquid and the interatomic potential directly from the point of view of wave vector space (k space). Although the Ornstein-Zernike equation was not originally derived from this point of view, this equation when transformed into the k-space representation has direct physical content, when coupled with a normal mode representation according to the approaches of Pines and Bohm (1952), and Percus and Yevick (1958). These normal modes are defined isothermally, and the relation to the dynamical modes of the liquid is discussed. The use of a simple k-space relationship between the transform of the Ornstein-Zernike direct correlation function and the transform, V_k , of the interatomic potential is explored. This leads to a correspondingly simple relationship between the structure factor and the interatomic potential. It is equivalent to a generalized Debye-Hückel equation and is expected to be valid only under special circumstances; namely, where the potential is long range in a particular sense and the small k behaviour of V_k is dependent mainly upon this long-range behaviour and relatively insensitive to details of the potential at short distances. It is noted that these conditions appear to be met reasonably well for the liquid alkali metals. The comparison of theory and experiment is somewhat uncertain because of incomplete experimental data on the structure factor as well as unresolved theoretical issues.     

Aluminum Hugoniot from model calculations including semicore electrons based on density functional theory

We present a method to obtain Hugoniot from model calculations based on density functional theory, and apply the method to aluminum Hugoniot. Technological advances have extended the experimental research of high energy density physics, and call for quantitative theoretical analysis. However, direct computation of Hugoniot from density functional theory is very difficult. We propose two step calculations of Hugoniot from density functional theory. The first step is molecular dynamics simulations with an ambient temperature for electrons. The second step is total energy calculations of a crystal with desired high temperatures for electrons and with the ambient temperature for electrons. We treated the semicore 2s and 2p electrons of aluminum as valence electrons only for the total energy calculations of the aluminum crystal. The aluminum Hugoniot from our model calculations is in excellent agreement with available experimental data and the previous density functional theory calculations in the literature.