A Lennard—Jones embedded—atom potential and its application to the study of melting

The nearest-neighbour Lennard-Jones potential from the embedded-atom method is extended to a form that includes more than nearest neighbours.The model has been applied to study melting with molecular dynamics.The calculated melting point,fractional volume change on melting,heat of fusion and linear coefficients of thermal expansion are in good agreement with experimental data.We have found that the second and third neighbours influence the melting point distinctly.     

A semiempirical formula describing the recoil yield in silicon

Krypton ions in the energy range 20–300 keV are used to generate recoiling atoms in silicon from thin layers evaporated on its surface. The recoil yields and the impurity distributions in the substrate have been measured as a function of several parameters (energy, thickness of the layer, incident dose). The results are used to propose a new formulation of the recoil yield based on the possibility, for both projectiles and recoiling atoms, to remove impurities previously introduced in silicon.The calculation fits very well the experimental results using displacement energies close to the generally admitted values     

Size effects of semiempirical large unit cell method in comparison with nanoclusters properties of diamond-structured covalent semiconductors

Self-consistent Hartree–Fock method within the framework of large unit cell (LUC) formalism using complete neglect of differential overlap (CNDO) is used to simulate size effects on nanoclusters of covalent crystalline diamond-structured semiconductor C, Si, Ge, and Sn using k=0 approximation. Three sizes are investigated namely 8, 64, and 216 atom LUCs. Cohesive energy, energy gap, valence band width, and hybridization orbitals are obtained from electronic structure calculations. Charge distribution, density of states, and orbital wave functions are also reported. Sensitivity analysis of the dependence of some of the calculated properties on model parameters is performed. Results revealed that electronic properties converge to some limit as the size of the LUC increases and that the 216 atoms LUC is very near to the bulk of these materials. Increasing LUC size or atomic number of covalent semiconductor removed some electronic cloud from bonding region to the spherical region around the atom. The same is true in going to higher energy levels. Increasing the size of LUC also resulted in a decrease of energy gap, increasing valance band width, and generally slightly increasing the cohesive energy. The model predicts energy gap reduction in going from ultra-small nanoclusters to the bulk of the four elements to be around 2 eV. The approximations imposed on the present model calculations leading to resemblance with nanoclusters properties in addition to the evidences of such resemblance such as orbital shapes and trends of data are discussed. Small nanoclusters are expected to have stronger directional bonds than in their bulk structure. The smallest cells (8 atoms) are found to be of a slightly longer lattice constant of the order 0.01, 0.1, 0.04, and 0.02 a.u. for diamond, silicon, germanium, and tin, respectively. X-ray form factors show a slight decrease of low-angle lines when we go to larger cells that was also found experimentally. To the best of my knowledge, this is the first systematic determination of covalent nanoclusters lattice constant and X-ray form factors variation with ultra-small nanocluster size.     

A composite model of the plastic flow of amorphous covalent materials

A model based on the data available in the literature on the computer simulation of amorphous silicon has been proposed for describing the specific features of the plastic flow of amorphous covalent materials. The mechanism of plastic deformation involves homogeneous nucleation and growth of inclusions of a liquidlike phase under external shear stress. Such inclusions experience plastic shear, which is modeled by glide dislocation loops. The energy changes associated with the nucleation of these inclusions at room and increased temperatures have been calculated. The critical stress has been found, at which the barrierless nucleation of inclusions becomes possible. It has been shown that this stress decreases with an increase in temperature. According to the calculations, the heterogeneous (homogeneous) plastic flow of an amorphous material should be expected at relatively low (high) temperatures. Above the critical stress, the homogeneous flow is gradually replaced by the heterogeneous flow.     

Density functional predictions of new silicon allotropes: Electronic properties and potential applications to Li-battery anode materials

In terms of first-principles density functional calculations, we investigate the stabilities and electronic properties of two hypothetical allotropes of silicon, the body-centered tetragonal (Bct) and monoclinic (M4) phases. The calculated electronic structures and phonon dispersions reveal that both phases are stable and have a band gap smaller than that of the diamond form of silicon by a factor of ∼2. We also discuss the possible applications of Bct and M4 phases as lithium-battery anode material.     

Comparative study of the semiempirical three-parameter potential energy functions for diatomic molecules

A comparative study is made of four three-parameter semiempirical potential energy functions for 32 electronic states of diatomic molecules and their ions:n ₂:X¹gS _g ⁺ ,B ³π_g,A ³ gS_u,C ³ _u,B′ ³ gS_u.a ¹ π_g, a′gS _u ^? ,Ω ¹δ_u N ₂ ⁺ :X ² gS _g ^gS +A ² π,C ² gS _u ⁺ ,B ² gS _u ⁺ CO:X¹gS⁺,a ³ π, a′³ gS_u,e ³ gS^?,d ³gD₁,A ¹π CO⁺:X²gS⁺,A ² π,B ²gS⁺ O₂:X³gS _g ^? ,B ³ gS_u,c ¹ gS _u ^? ,b ¹gS _g ^s ,a ¹ δ_g,c ³ δ_u O ₂ ⁺ :X ²π_g,A ² π_g, a¹ π_g,b ⁴ gS _g ^? A program for numerically integrating the radial Schrödinger equation by the Cooley method is worked out. Certain additional units are introduced to conserve computer time. The resulting vibrational levels are compared with the experimental levels for all the electronic states studied. It is concluded on the basis of this analysis that it is not possible to describe equally well all the electronic states of various molecules on the basis of any single three-parameter potential function. A method for choosing a potential function for describing some particular electronic state of a diatomic molecule is proposed.     

Ag（110）表面声子谱的分析型EAM模型计算

应用晶格动力学，结合分析型EAM模型，计算了Ag(110)表面声子频率和振动极化方向，通过比较弛豫与未弛豫表面的计算结果，发现弛豫后的结果与He原子散射实验数据符合得很好，表面振动的极化局域特征符合表面的二维对称性，沿方向的S2和S3表面模也和实验结果—致. 关键词： 表面声子谱 弛豫 EAM 极化     

Application of the correlation method to analyze deformations in transparent materials

The scheme of elastic stress visualization in transparent materials (Plexiglas) by a change in optical path is proposed. The optical path gradient was measured using the correlation method. A model experiment was performed at various configurations of transverse static loads on a Plexiglas beam. It was shown that the displacement field of the background structure corresponds to stress diagram at a given beam load scheme. For the process of point heating of quartz glass, the correlation method is compared to the method based on the photoelasticity effect.     

Calculation of the surface energy of fcc metals with modified embedded-atom method

The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, A1, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, A1, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.     

fcc金属层错能的EAM法计算

采用嵌入原子法(EAM)计算了Cu，Ag，Au，Ni，Al，Rh，Ir，Pd，Pt和Pb等10种面心立方(fcc)金属的层错能，除Rh和Ir两种金属外，其他金属的计算结果和实验结果基本一致. 关键词： 面心立方金属 层错能 EAM     

A semiempirical method of applying the dechanneling correction in the extraction of disorder distribution

The application of single, plural or multiple scattering theories to the determination of defect dechanneling in channeling-backscattering disorder measurements is re-examined. A semiempirical modification to the method is described that results in making the extracted disorder and disorder distribution relatively insensitive to the scattering model employed. The various models and modifications have been applied to the 1–2 MeV He⁺ channeling-backscatter data obtained from 20–80 keV H⁺ to Ne⁺ bombarded Si, GaP and GaAs at 50 K. and 300 K.     

A new method to study complex materials in solid state chemistry: application to chalcogenide materials

We show that a combined application of Mössbauer spectroscopy and other experimental tools such as X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy and nuclear magnetic resonance provides a coherent picture of the local electronic structure in chalcogenide materials. In order to develop this idea we propose an analysis of the Sn, Sb and Te local electronic structures for three different systems of materials. The first example concerns the In–Sn–S system. We show that Li insertion in In₁₆Sn₄S₃₂ leads to changes of the Sn oxidation states from Sn(IV) to Sn(II). The second example concerns materials of the Tl–Sb–S system. We show that variations of the ¹²¹Sb Mössbauer isomer shift and surface of the first peak of the X‐ray absorption spectra at the Sb L_III edge can be linearly correlated because of the main influence of the Sb 5s electrons. This is explained by changes in the local environment of the Sb atoms. The last example concerns the crystalline phases of the Tl–Sn–Te system. The formal oxidation numbers of the Te atoms are determined from ¹²⁵Te Mössbauer spectroscopy and X‐ray photoelectron spectroscopy. They are related to the different types of bonds involving the Te atoms in the Tl–Sn–Te compounds.     

一种简捷求解定态薛定谔方程的方法:科尔-霍普夫变换法

介绍一种求解各个能级及定态波函数的简捷方法,即借助于科尔-霍普夫(Cole-Hopf)变换法,将给定势函数的定态薛定谔方程变换成黎卡提(Riccati)方程,以求出各个能级及定态波函数.并以谐振子、球谐振子、氢原子、P schl-Teller势、Morse势、Hulth啨n势、双原子分子的三参量势函数、同调谐振子为实例,给出求解方法及结果.     

The scattering approach: Application to the conductance of silicon nanograins

The purpose of this study is the assessment of the properties of the conductance of silicon nanostructures. The calculation method, taken from the recent chemical literature, is based on the scattering approach and on the extended Hückel theory and is further simplified by the parametrization of the contact potentials in terms of the Hamiltonian of the active region. The structures considered are crystalline columnar grains sandwiched between two adsorbing contacts and their size reaches 400 atoms. The calculations analyse the structural parameters and the electronic configuration of the grains and examine the relationship between this quantity and the conductance. It is shown that the conductance depends on the energy difference across the occupied energy levels and for this reason has the same dependence on the grain size and shape as the binding energy. This allows an unified formulation of the electronic and transport properties.     

A potential integration method for Birkhoffian system

This paper is intended to apply the potential integration method to the differential equations of the Birkhoffian system. The method is that, for a given Birkhoffian system, its differential equations are first rewritten as 2n first-order differential equations. Secondly, the corresponding partial differential equations are obtained by potential integration method and the solution is expressed as a complete integral. Finally, the integral of the system is obtained.