Al12N、Al12B团簇结构和电子性质的密度泛函计算

利用密度泛函理论研究了Al12N和Al12B团簇的原子结构和电子性质,通过各种异构体的比较,发现两种掺杂团簇的最低能量结构都是完好的二十面体(Ih)结构,N(B)原子占据在二十面体的中心.高对称性团簇形成稀疏离散的电子态密度和大的电子能隙.在Al-N之间发生较大的电荷转移.因此我们建议把Al12N团簇看作是碱金属超原子,Al12B团簇看作是卤素超原子,用来构造团簇组装固体.     

双氮原子掺入二氧化钛电子结构的第一原理研究

采用基于第一性原理的平面波超软赝势方法计算研究了双N原子掺入金红石相TiO_2的几何结构和电子结构.通过比较三种可能的掺杂方式的总能发现,两个氮原子占据两个相邻的B原子位置时具有最稳定的结构.电子结构分析表明,双N原子掺杂TiO_2出现了杂质能级,三种结构的能带间隙均减小,其中杂质原子最近邻占位时,带隙最小,随着两个杂质原子的距离增大,带隙会逐渐变大.     

First principles study of the structural,electronic, mechanical and superconducting properties of WX (X=C,N)

The structural, electronic, mechanical and superconducting properties of tungsten carbide (WC) and tungsten nitride (WN) are investigated using first principles calculations based on density functional theory (DFT). The computed ground state properties, such as equilibrium lattice constant and cell volume, are in good agreement with the available experimental data. A pressure induced structural phase transition is observed in both tungsten carbide and nitride, from a tungsten carbide phase (WC) to a zinc blende phase (ZB), and from a zinc blende phase (ZB) to a wurtzite phase (WZ). The electronic structure reveals that these materials are metallic at ambient conditions. The calculated elastic constants obey the Born-Huang criteria, suggesting that they are mechanically stable at normal and high pressure. Also, the superconducting transition temperature is estimated for the WC and WN in stable structures at atmospheric pressure.     

A first-principle study of the structural and electronic properties of amorphous Cu-Zr alloys

The atomic and electronic structures of amorphous CuxZr100-x(x=36,46,50,56,64) alloys were simulated using first-principle calculations within a 400-atom supercell.The pair correlation function,coordination numbers,local cluster structures and electronic density of states were analyzed.Reasonable agreements between the theory and the experiments were obtained.The amorphous alloys exhibit different local cluster structures and can all be explained with cluster formulas [cluster](glue)1,3,where the clusters a...     

Ab-initio study of structural and electronic properties of AlAs

The structural properties, i.e. equilibrium lattice constant, transition pressure, bulk modulus and its pressure derivatives, together with electronic properties, i.e. energy bands, Compton profile and autocorrelation function, of AlAs are presented in this work. The linear combination of atomic orbitals (LCAO) method of the CRYSTAL code was applied considering the Perdew–Burke–Ernzerhof correlation energy functional and Becke's ansatz for the exchange. The total energy of AlAs as a function of primitive cell volume has also been calculated for the zincblende (B3), nickel arsenide (B8), sodium chloride (B1) and cesium chloride (B2) phases. Structural parameters of the B3, B8, B1 and B2 phases are determined. The calculated structural parameters are found to be in good agreement with the results of previous investigations. The spherically averaged theoretical values of Compton profile are in good agreement with an earlier measurement. The LCAO calculation shows an indirect band gap of 1.85?eV, in reasonable agreement with earlier data. On the basis of the equal-valence-electron-density Compton profile, it is found that AlAs is more ionic compared to AlSb.     

Theoretical study of BeO: structural and electronic properties

The pseudopotential method is used to examine the static structural and electronic properties of BeO. At zero pressure, the wurtzite phase is found to be more stable in energy than the zincblende. At high pressure, we predict a phase transformation into an insulating rocksalt structure. The calculated charge density for the valence electrons is in good agreement with experiment.     

3d过渡金属元素掺杂Al12N12纳米线几何结构和电子性能的第一性原理研究

基于密度泛函理论的第一性原理计算方法,系统地研究了不同3d过渡金属元素(Sc、Ti、V、Cr、Mn、Fe、Co和Ni)掺杂Al₁₂N₁₂纳米线的几何结构、稳定性和电子结构.结果表明：所有掺杂体系均是热力学稳定的;掺杂Ni时体系保留了原有的非磁性间接带隙半导体特性;当掺杂其它原子(Sc、Ti、V、Cr、Mn、Fe、Co)时体系仍然保持为半导体,但带隙明显减小.掺杂过渡金属原子对于Al₁₂N₁₂纳米线的电子结构具有明显的调控作用,在能带调控和光电方面有潜在的应用前景.     

A study of 12C and 28Si interactions with heavy emulsion targets

This paper presents some general characteristics of totally disintegrated events observed in the interactions of Silicon and Carbon with Ag/Br nuclei. The events with heavy particle multiplicity greater than or equal to twenty-eight, i. e., N_h ≥ 28 were analyzed. The probability of occurrence of central collision events is found to increase with the mass of the projectile and total projectile energy. The multiplicity distributions are described quite well by a Gaussian curve. The variation in the mean multiplicity of grey, black, heavy, and shower particles with projectile mass is being discussed. Average compound particle multiplicity is found to increase with the mass of the projectile.     

Geometric and electronic structures of B12C6N6 fullerene

An electron deficient fullerene B₁₂C₆N₆ is studied by using ab initio calculations. The structure is generated by replacing N with C in the B₁₂N₁₂ cage to ensure only B–C and B–N bonds are formed. All the possible isomers are optimized and the low energy structures are determined. C and N atoms in the low energy isomers are inclined to segregate and form B₂C₂ and B₂N₂ squares. Natural bond analysis shows that the atomic orbitals of B, C and N in this cage hybrid approximately in sp^2.3 and then form B–C and B–N bonds. The 2p orbitals perpendicular to the cage surface are partially occupied and the molecular orbitals formed by these orbitals are highly delocalized. The natural charge on N is about −1.17 in both B₁₂N₁₂ and B₁₂C₆N₆, and the charge on C is −0.72 to −0.60. The molecular orbital compositions show that the B–N bonds are the same in B₁₂N₁₂ and B₁₂C₆N₆, and the B–C bonds possess stronger covalent character. The HOMO of B₁₂C₆N₆ is formed by 2p of B and C, and the LUMO is formed by 2p of C. The energy gap of C₂₄, B₁₂N₁₂ and B₁₂C₆N₆ is 2.52, 6.84 and 3.22 eV, respectively.     

First principles study of structural,electronic and thermoelectric properties of skutterudite GdFe4As12 compounds

The full potential linearized augmented plane wave (FP-LAPW) method has been used to investigate structural, electronic and thermoelectric properties of Skutterudite GdFe₄As₁₂ compounds in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) and (GGA+U). The ground-state properties are determined in the cubic structure (Im-3, space group 204). It is found that the most stable phase structure of GdFe4As12 compounds is the ferromagnetic phase and it shows a semi-metallic behavior with narrow gap. The calculation of the density of states near the Fermi level shows the compound to be suitable for the effective thermoelectric application. In addition, the high Seebeck coefficient value is obtained in the n-type region than p-type, indicating the prominence of n-type doping in filled skutterudite GdFe₄As₁₂.     

Tight-binding study of structural and electronic properties of silver clusters

Tight-binding model is developed to study the structural and electronic properties of silver clusters. The ground state structures of Ag clusters up to 21 atoms are optimized by molecular dynamics-based genetic algorithm. The results on small Ag_n clusters (n = 3-9) are comparable to ab initio calculations. The size dependence of electronic properties such as density of states, s-d band separation, HOMO-LUMO gap, and ionization potentials are discussed. Magic number behavior at Ag₂, Ag₈, Ag₁₄, Ag₁₈, Ag₂₀ is obtained, in agreement with the prediction of electronic ellipsoid shell model. We suggest that both the electronic and geometrical effect play significant role in the coinage metal clusters. Received 7 August 2000     

外掺非典型富勒烯C64Si的几何结构和电子性质计算研究

采用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient approximation, GGA)对非典型富勒烯C64Si的几何结构和电子性质进行计算研究,发现在C64Si可能稳定存在的四种同分异构体中,Si原子吸附在三个直接相邻五边形的公共原子处形成的外掺杂结构是热力学最稳定的结构,即文中定义的C64Si-1,这和Ge等人对 Si原子在C28笼子外部最稳定位置的预测相一致.通过对C64Si-1的能级图、轨道分布和态密度图的分析可知:Si原子的原子轨道对电子最低未占据轨道的贡献比较大,而对电子最高占据轨道的贡献比较小,但是Si原子的局部态密度对C64Si-1整体态密度的影响非常小.对C64Si-1的亲和能和电离能分析得知:外掺Si原子之后,笼子的得电子能力和失电子能力都有所降低.     

New self-intercalated C28, Ti@C28, and Zn@C28 hyperdiamonds: Crystal structure and elastic and electronic properties

New dense crystal forms of small fullerenes with unusual (combined covalent-van der Waals) atomic bonding, namely, the so-called self-intercalated hyperdiamonds (SIHDs) are suggested. The SIHD systems consist of C₂₈ fullerenes and Ti@C₂₈ and Zn@C₂₈ endofullerenes compacted into diamond lattices, in which the voids are filled with the same fullerenes. The electron density functional method in the tight binding approximation is applied to simulate the structure and to calculate the elasticity parameters, electronic characteristics, and formation energy of C₂₈, Ti@C₂₈, and Zn@C₂₈ SIHDs. It is found that the values of the bulk modulus of the SIHDs are much (2.3–2.7 times) greater than those of the initial hyperdiamonds. It is found that the C₂₈ SIHD is a semiconductor with a band gap of about 1.3 eV, whereas the Ti@C₂₈ and Zn@C₂₈ SIHDs exhibit metal-like electronic spectra. For the alternative diamond-like C₂₈ phases (hyperdiamond, hyperlonsdaleite, and SIHD), the theoretical shape of the x-ray diffraction spectra is calculated.     

多壳层铜纳米线结构和电子特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,系统地研究了多壳层Cu纳米线的稳定结构和电子特性.得到不同线径多壳层Cu纳米线的平衡态晶格常数相差不大,都表现出金属特性,且其单原子平均结合能和量子电导随着纳米线直径的增加而增加.纳米线中内壳层Cu原子表现出体相结构Cu原子相似的电子特性,而表面壳层由于配位数的减少,其3d态能量范围变窄且整体向费米能级发生移动.电荷密度分析表明,相对于体相Cu晶体中原子间的相互作用,纳米线表面壳层Cu原子与其最近邻原子间的相互作用明显增强.     

First-principles study on the structural and electronic properties of ultrathin ZnO nanofilms

Using first-principles density-functional calculations, we have studied the structural and electronic properties of ultrathin ZnO {0001} nanofilms. The structural parameters, the charge densities, band structures and density of states have been investigated. The results show that there are remarkable charge transfers from Zn to O atoms in the ZnO nanofilms. All the ZnO nanofilms exhibit direct wide band gaps compared with bulk counterpart, and the gap decreases with increased thickness of the nanofilms. The decreased band gap is associated with the weaker ionic bonding within layers and the less localization of electrons in thicker films. A staircase-like density of states occurs at the bottom of conduction band, indicating the two-dimensional quantum effects in ZnO nanofilms.     

First principles study of structural,elastic and electronic structural properties of strontium chalcogenides

Structural, elastic and electronic properties of strontium chalcogenides SrX (X = O, S and Se) in the B1 (NaCl) and B2 (CsCl) phases were investigated in the present work. The calculations were performed using density functional theory (DFT) within generalized gradient approximation (GGA) using scalar relativistic Vanderbilt-type ultrasoft pseudopotentials. Results for structural properties of both phases, the pressure at which transition from B1 to B2 phase occurs and the volume compression ratio for each compound were reported. Elastic properties of the B1 phase of these compounds, such as elastic constants C₁₁, C₁₂, and C₄₄, shear modulus (G), Young's modulus (E), Poisson's ratio (σ), Kleinman parameter (ξ), and anisotropy factor (A) were also calculated at ambient conditions. The band gaps and density of states were studied too for the B1 structure of these compounds. The present results were compared with the available experimental and other theoretical results, and found to be in satisfactory agreement with them.