Stillinger–Weber parameters for In and N atoms

A Stillinger–Weber (SW) type empirical potential for InN is presented in order to realistically describe the atomic structures of In_xGa_1−xN alloys and to calculate the deformation induced by In-rich clusters in InGaN/GaN quantum wells. The SW parameters are optimized by fitting the lattice parameters and the elastic constants of InN in wurtzite and zinc-blende structure, and comparing the energy dependence of the atomic volume in the two configurations. With these parameters, the distribution of indium in random, ordered and cluster configurations of InGaN alloys is investigated. Bond lengths, atomic energies, formation enthalpies and local deformation are calculated and compared with the experimental values.     

Macroscopic-microscopic theory of semi-spheroidal atomic cluster

The macroscopic-microscopic method is adapted to atomic clusters deposited on a surface. Analytical relationships for the deformation-dependent liquid drop model (LDM) energies of oblate and prolate semi-spheroidal atomic clusters have been obtained. A superdeformed prolate semi-spheroid is the most stable semi-spheroidal shape within LDM. It is also the shape with maximum degeneracy of quantum states of the semi-spheroidal harmonic oscillator used to compute the shell and pairing corrections. The microscopic corrections as well as total deformation energy show parabolic valley and ridges of the potential energy surfaces in the plane (deformation, number of atoms). The ground state and isomeric state deformation of clusters of various sizes depends on the interplay between the minima of LDM and shell correction energies.     

一种适用于原子团簇的多体展开新方案: 以氮团簇为例

多体展开方法虽然已经广泛地用于估算弱相互作用体系的能量,但是其并不适用于计算共价团簇和金属团簇的能量. 本文提出了一种适用于计算共价体系能量的相互作用多体展开(IMBE)方法. 在相互作用多体展开方法中,体系的能量表示为孤立原子的能量及该原子与其他周围原子间相互作用的和. 首先将该方法应用于计算氮团簇的能量,且多体展开截断至四体项. 结果表明：与传统的多体展开方法相比,相互作用多体展开方法可以显著地降低能量误差. 另外,以密度泛函理论计算结果为参考,相互作用多体展开方法估算能量的误差不依赖于体系的大小和结构,说明相互作用多体展开方法比较适合用于估算共价相互作用大体系的能量.     

飞秒强激光作用下Ar原子团簇离子能谱计算

研究了飞秒强激光与Ar原子团簇相互作用时的电离机制及库仑爆炸过程,建立了一个简化的模型计算相互作用产生的离子能谱,计算结果与实验结果较为吻合,可以较好地解释离子能谱高能端的主要特征。     

Dynamic characteristics of the low-temperature decomposition of the C20 fullerene

A novel algorithm has been proposed for simulating thermal decomposition of atomic clusters at such low temperatures that the corresponding lifetimes are macroscopic and, hence, standard molecular dynamics algorithms are inapplicable. The proposed algorithm is based on a combination of the molecular dynamics and Monte Carlo techniques. It has been used to calculate the temperature dependence of the lifetime of the thermalized C₂₀ fullerene until it decomposes at T=1300–4000 K. The frequency factor and activation energy of the decomposition have been determined. It has been demonstrated that the temperature dependences of the lifetimes of the heat-insulated and thermalized fullerenes differ significantly.     

小尺寸铜团簇冷却与并合过程中结构变化的原子尺度研究

研究Cu_N（N=57,58,59）熔融铜团簇在冷却过程以及300 K时两个具有二十面体结构Cu₅₅团簇在并合过程中的结构变化.对这些小尺寸团簇的结构变化采用基于嵌入原子方法的正则系综分子动力学进行计算机模拟.通过对模拟结果的分析表明,小团簇的冷却和并合过程存在阶段变化的特点.降温过程中Cu_N（N=57,58,59）团簇的原子运动及其微观结构变化表现出较大差异,由此导致这三类团簇内原子排布的不同,其中Cu₅₉团簇结构的有序程度最低.在两个Cu₅₅团簇并合早期阶段,这两个团簇相接触后发生变形导致原子位置出现较大改变,在随后的并合过程中,原子扩散引起原子局部位置调整导致所并合体系的结构发生变化.远离两个团簇接触区的原子仍保持其并合前的结构. 关键词： 团簇 分子动力学 计算机模拟 表面     

A molecular dynamics study of the structural change differences between Au225 and Au369 clusters on MgO surfaces at low temperature

The differences in structural change between Au₂₂₅ and Au₃₆₉ clusters with their (111) facets supported on MgO(100) surfaces at 5 K are studied by using molecular-dynamics simulations with the atomic interchange potentials of the Au/MgO interface. The parameters are obtained from the ab initio energies using the Chen-Möbius inversion method. Analyses of the pair distribution functions show that the two Au clusters use different deformation processes to adjust the distances between the interface atoms, owing to the misfit between the atom distances among the clusters and the substrates. The local structural changes are identified by atomic density profiles.     

Energy spectra and temperature distributions of clusters produced during ion-beam sputtering of metals

A method for evaluating the energy spectra and temperature dependences of the yield of neutral and charged clusters that consist of N≥5 atoms and are produced by ion bombardment of metals is proposed. The results are presented in the form of simple formulas. Theoretical energy spectra of clusters emitted as a result of bombarding niobium, tantalum, and iron targets by atomic ions of gold or xenon and temperature dependences of the yield of silver clusters produced by bombarding the targets with xenon ions are compared with experimental data.

     

General axial shapes of sodium clusters

The shell correction method is applied to calculate the shapes and binding energies of Na clusters. The axial equilibrium shapes are calculated by minimizing five deformation parameters simultaneously. Strong deviations from spheroidal shapes including reflection asymmetric ones are found. The influence of cluster deformation on the separation energies and ionization potentials and on the splitting of the photo - resonance are compared with the available experimental data. The N-dependence of the cluster shape and its relation to the N- and Z-dependences of the nuclear shape is discussed.     

Deposition of Ni<Subscript> 13</Subscript> and Cu<Subscript> 13</Subscript> clusters on Ni(111) and Cu(111) surfaces

The soft deposition of Ni₁₃ and Cu₁₃ clusters on Ni(111) and Cu(111) surfaces is studied by means of constant-energy molecular-dynamics simulations. The atomic interactions are described by the Embedded Atom Method. It is shown that the shape of the nickel clusters deposited on Cu(111) surfaces remains rather intact, while the copper clusters impacting on Ni(111) surfaces collapse forming double and triple layered products. Furthermore, it is found that for an impact energy of 0.5 eV/atom the structures of all investigated clusters show the lowest similarity to the original structures, except for the case of nickel clusters deposited on a Cu(111) surface. Finally, it is demonstrated that when cluster and substrate are of different materials, it is possible to control whether the deposition results in largely intact clusters on the substrate or in a spreading of the clusters. This separation into hard and soft clusters can be related to the relative cohesive energy of the crystalline materials.     

Energy of Clusters Emitted During Ion Sputtering of a Metal

A procedure for calculating the energy spectra of clusters with numbers of atoms N 5 during ion sputtering of a metal is suggested. The results are presented in the form of simple formulas. The energy distributions of clusters in the bombardment of niobium and iron by atomic gold and xenon ions, calculated in the present work, are compared with the available experimental data.     

Dynamics of free and embedded lead clusters in intense laser fields

Lead clusters are exposed to strong femtosecond light pulses. The dependence of the recoil energy on the charge state of the atomic ion is now investigated using a new detection setup, i.e., a Thomson analyser. First results show that in contrast to laser-induced overdense plasmas at surfaces the recoil energy distribution appears much narrower. Comparing free lead clusters with lead clusters embedded in large helium droplets, the charging dynamics show distinct differences on the femtosecond time scale. In the embedded case the maximum ionization enhancement is reached earlier.     

密度泛函理论对CoBen(n=1—12)团簇结构和性质的研究

采用密度泛函理论中的广义梯度近似(GGA)对CoBe_n(n=1—12)团簇的几何构型进行优化，并对能量、频率和磁性进行了计算，同时考虑了电子的自旋多重度.得到了CoBe_n(n=1—12)团簇最低能量结构的自旋多重度是2和4.在CoBe_n(n=1—12)团簇中，Co原子的磁矩出现了奇偶振荡，当n=6时，Co原子的4s，3d和Be原子的2s，2p较强杂化、Co-Be键长的减小以及对称性的降低导致Co原子的磁矩最小.通过对CoBe_n(n=1—12)团簇电子性质的分析，得出了掺杂可以增强团簇稳定性和有利于增加合金化学活性的结论.n=5，10是团簇的幻数. 关键词： n团簇')" href="#">CoBe_n团簇 自旋多重度 磁矩 电子性质     

Density functional study of structural and electronic properties of Al<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>P (2 ≤ <Emphasis Type="Italic">n</Emphasis> ≤ 12) clusters

Low-lying equilibrium geometric structures of Phosphorus-doped aluminum cluster Al _n P (n = 2–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee-Yang-Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated for the ground-state structures within the GGA. It is observed that symmetric structures with the P atom occupying a peripheral position are lowest-energy geometries of Al _n P (n = 2, 4–11), while the P impurities of Al₃P and Al₁₂P prefer to occupy internal sites in the aluminum clusters. Generalized gradient approximation extends bond lengths as compared to the LSDA lengths. The odd-even oscillations in the dissociation energy, the second differences in energy, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within both GGA and LSDA. The stability analysis based on the energies clearly shows the clusters with an even number of valence electrons are more stable than clusters with odd number of valence electrons.     

Physical mechanism of swift heavy ion irradiation effect in graphene

ABSTRACT

The damage production induced by swift heavy ion irradiation in single-layer graphene (SLG) is investigated by molecular dynamics method. By given energy to a cylindrical region, the latent track consisting of nanopore and non-six-member rings can be produced, which depends on the electronic energy loss (dE/dx). For SLG, the minimum value needed to generate defects lies in 6.5–10?keV/nm. The latent track formation begins with the decomposition of the structure in energy deposition region until the atomic fragments escape from the surface and gradually decompose into atomic clusters. At the same time, the structure of system also changes. The source power of this phenomena is the accumulation and outward propagation of atomic stress in energy deposition region.     

Simulation of the interaction of bipartite bimetallic clusters with low-energy argon clusters

Molecular-dynamics simulation of the evolution of bipartite bimetallic clusters consisting of 390 atoms during bombardment by Ar_n (n = 1, 2, 13) clusters with initial energies from 1 eV to 1.4 keV is performed. Binary Cu–Au and Ni–Al clusters consisting of equal atomic fractions of corresponding elements were used as a target. As a result of simulation, the temperatures, changes in the potential energy, sputtering yields, and intensities of collision-stimulated displacement of atoms through the interface of monometallic parts of binary clusters, depending on the size and energy of incident particle, are obtained.

     

The electronic structure of arbitrarily shaped atomic clusters: A formal MSW approach

In this paper a formal MSW approach is established to calculate the energy levels of atomic clusters and molecules. It is shown that the standard secular equation is formally preserved, though the muffin-tin approximation is replaced by the only assumption that the total potential is a sum of (possibly overlapping) atomic contributions. The transition matrix still contains all information about the scattering properties of the atoms, but is no longer diagonal in the angular momentum indices.     

Characteristics of the backscattering of moderate-energy electrons by solids having different atomic numbers

The coefficient of backscattering of primary electrons is discussed as a function of their energy and atomic number Z. The amplitude of the wave function obtained in the first Born approximation and the Thomas-Fermi atom model are used to calculate the constant for screening of the electric field of the nucleus by atomic electrons. The theoretically calculated integral backscattering coefficients of primary electrons are compared with the experimental values in the range 12<Z<92 for primary electron energies of 10 and 40 keV. Possible applications of these results are indicated. Zh. Tekh. Fiz. 69, 40–45 (June 1999)