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.     

Silver oligomer and single fullerene electronic properties revealed by a scanning tunnelling microscope

Clusters on surfaces have been investigated with low-temperature scanning tunnelling microscopy and spectroscopy. Constant current spectra acquired on Ag oligomers and one-dimensional chains on a Ag(111) reveal a single resonance peak whose energy shifts towards the Fermi level with increasing cluster size. Next, controlled and reproducible contact between a STM tip and a C₆₀ molecule adsorbed on Cu(100) is reported. The transition from tunnelling to contact is discussed in terms of local heating of the tip-molecule junction.     

Orientation effect on the electronic transport properties of C24 fullerene molecule

The transport properties of the cage-like molecule depend on its orientation between the electrodes, but the investigation on the mechanism has not been found. Using first-principle density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism for quantum transport calculation, we study the electronic transport properties of C₂₄ fullerene molecule with different orientations in Au–C₂₄–Au two-probe system. The effects of k-point sampling on the Brillouin zone are explored. Our results show that the negative differential resistance of C₂₄ molecule is found in such a system and can be tuned by the molecule's orientation in the two-probe system. We also proposed a mechanism for it. The I–V characteristic under bias voltage is determined. The present findings could be helpful for the application of the C₂₄ molecule in the field of single molecular devices or nanometer electronics.     

Location of muonium and hydrogen in C60 fullerene and associated electronic structure and hyperfine properties

The unrestricted Hartree-Fock (UHF) procedure is used to investigate the locations, associated electronic structures and hyperfine interactions for muonium and hydrogen in C₆₀ fullerene. Our results indicate that from total energy considerations, in keeping with earlier investigations, the exohedral model has the lowest energy. However, the energies of the endohedral model involving the muonium (hydrogen) inside the fullerene and bonded to one of the carbon atoms, and of the muon at the center are found to be almost equal, contrary to earlier results. The hyperfine interaction constant for the endohedral site is in good agreement with that required to explain the lower observed muon spin-rotation (SR) frequency in the C₆₀-muonium system. The same appears to be the case for the exohedral model. However, there seems to be some uncertainty about the theoretical result in the latter case due to significant admixtures of higher spin states in the UHF wave-function. Additionally, in solid fullerene, the calculated location of the muonium for the exohedral model is such that it could be bonded to two fullerene molecules and therefore a muonium attached to a simple fullerene may not be representative of the exohedral state. This feature as well as the difficulty for the exohedral model of explaining the observed equality of the correlation times for relaxation effects associated with both SR and¹³C relaxation times in nuclear magnetic resonance (NMR) experiments suggests that the endohedral model for muonium cannot at present be ruled out as a viable model in favor of the exohedral model. Possible avenues for future investigations to resolve some of the problems for both exohedral and endohedral models are discussed. Results obtained for muonium at the center of fullerene are presented and compared to the features of the observed high frequency SR signal, and possible improvements in theory are discussed.     

Time-dependent Hartree-Fock calculation of 12C + 12C with a realistic potential

We have used a realistic single-panicle K-matrix model to compute the head-on scattering of ¹²C + ¹²C at incident projectile lab energies of 3.2, 6.4, 12.8, 19.2, 25.6, 32, 51.2 and 64 $\text{MeV}\text{nucleon}$, above the Coulomb barrier, in the time-dependent Hartree-Fock approximation. Direct and exchange Coulomb forces as well as spin-orbit forces are included. A large deformed harmonic oscillator basis is used. Spatial density and current distributions at various times are shown. The outgoing energy is found to be E₀ = 0.8E_in?28 (MeV), in the c.m. system. Fusion and fully relaxed scattering are observed at low energy. Some compression is seen at higher energies but no shock waves can be detected. Consequences for heavy-ion reactions are discussed.     

L12型铝合金的结构、弹性和电子性质的第一性原理研究

运用第一性原理方法研究了L12型铝合金相Al3Sc和Al3Zr的晶体结构、电子结构和弹性.结合能和形成能的计算表明,两种合金具有较强的合金化能力,且Al3Zr较Al3Sc具有更强的结构稳定性.电子结构分析表明,费米能级以下较多的价电子数决定了Al3Zr具有较强的结构稳定性.计算并分析比较了两种合金相的单晶弹性常数(C11,C12和C44)以及多晶弹性模量(体弹性模量B、剪切模量G、杨氏模量Y、泊松比ν和各向异性因子A).通过对比实验和其他理论计算结果,进一步分析和解释了两种合金相的力学性质.     

Al和N共掺p型Zn1-xMgxO电子结构的第一性原理计算

采用密度泛函理论下的第一性原理平面波超软赝势方法,对Zn1-xMgxO超晶胞和掺杂Al,N后的Zn1-xMgxO超晶胞分别进行了优化计算.结合广义梯度近似计算了Al和N共掺杂后Zn1-xMgxO的能带结构、电子态密度和Mulliken电荷布居分布.计算表明:掺入N原子的2p态电子为Zn1-xMgxO价带顶提供空穴载流子,使Zn1-xMgxO价带顶向高能方向移动;掺入Al原子的3p态电子则与N原子的2p态电子在费米能级附近发生轨道杂化,使费米能级处价带能级展宽,Al和N共掺杂可获得p型Zn1-xMgxO.     

Optical properties of B x N y C z monolayers

We apply first-principles methods, based on the density functional theory, to investigate the optical properties of B _x N _y C _z hybrid monolayers containing domains. It is observed that the energy structure of such compounds exhibits bound excitons in the near-infrared region. Moreover, such compounds present an extraordinary absorptive capacity in the visible spectrum, which makes them important candidates for future solar cells applications.     

Electron delocalization and dimerization in solid C59N doped C60 fullerene

Electron spin resonance and ab initio electronic structure calculations show an intricate relation between molecular rotation and chemical bonding in the dilute solid solution. The unpaired electron of C59N is delocalized over several C60 molecules above 700 K, while at lower temperatures it remains localized within short range. The data suggest that below 350 K rigid C59N-C60 heterodimers are formed in thermodynamic equilibrium with dissociated rotating molecules. The structural fluctuations between heterodimers and dissociated molecules are accompanied by simultaneous electron spin transfer between C60 and C59N molecules. The calculation confirms that in the C59N-C60 heterodimer the spin density resides mostly on the C60 moiety, while it is almost entirely on C59N in the dissociated case.     

Beta decay of12B and12N to the first excited state of12C (4.44 MeV)

The branching ratios of the beta-decay of¹²B and¹²N to the 4.44 MeV state in¹²C were determined by (βγ-coincidences to be (1.182±0.019)% and (1.898±0.032)% of the total rate, resp. This givesft ^?=(1.407±0.023) · 10⁵ s andft ⁺=(1.406±0.024) · 10⁵ s. For theft-asymmetryδ=(ft ⁺/ft ^?)?1 the valueδ=?(1±14) · 10^?3 was obtained. This is in contrast to other GT mirror transitions which show positiveδ of a few percent.     

B0.44Co0.27N0.29化合物的合成、表征和性能

以硼酸和三聚氰胺为原料,利用化学法、真空热处理及高温高压技术对BCN化合物的形成、结构及相变进行了研究.在真空10-3Pa条件下,经1273K高温热处理得到非晶B-C-N前驱物.这种前驱物在920K以下为绝缘体,在920K由绝缘体转变为非晶半导体.在973-1003K和1013-1073K范围这种非晶半导体表现出不同的电导-温度关系,电导激活能分别为0.34eV和1.10eV,表明在两个不同的温度区域这种非晶半导体的导电机构不同.将这种前驱物在3.5GPa,经1473K退火40min后由非晶态转化为单相六方结构的B-C-N晶体,其成分为B0.44C0.27N0.29,晶格常数为a=0.2515nm,c=0.6684nm.六方B0.44C0.27N0.29晶体在1330,1364,1588和1617cm-1出现四个强的Raman散射峰,其中1330和1617cm-1被认为是六方B0.44C0.27N0.29晶体特征Raman散射峰.     

B0.44C0.27N0.29化合物的合成、表征和性能

以硼酸和三聚氰胺为原料，利用化学法、真空热处理及高温高压技术对BCN化合物的形成、结构及相变进行了研究．在真空10^-3Pa条件下，经1273K高温热处理得到非晶B-C-N前驱物．这种前驱物在920K以下为绝缘体，在920K由绝缘体转变为非晶半导体．在973-1003K和1013-1073K范围这种非晶半导体表现出不同的电导一温度关系，电导激活能分别为0．34eV和1．10eV，表明在两个不同的温度区域这种非晶半导体的导电机构不同．将这种前驱物在3．5GPa，经1473K退火40min后由非晶态转化为单相六方结构的B-C-N晶体，其成分为B0.44C0.27N0.29，晶格常数为a=0．2515nm，c=0．6684nm．六方B0.44C0.27N0.29晶体在1330，1364，1588和1617cm^-1出现四个强的Raman散射峰，其中1330和1617cm^-1被认为是六方B0.44C0.27N0.29晶体特征Raman散射峰.     

Shape and electronic structure of organoboron nanoparticles prepared by the high-temperature pyrolysis of carborane C2B10H12

Scanning tunneling microscopy and spectroscopy are used to determine the shape and electronic structure of organoboron nanoparticles formed during high-temperature pyrolysis of C₂B₁₀H₁₂ carborane vapor. Spherical, lenticular, and shapeless nanoparticles are found. Spherical and lenticular particles exhibit metallic conduction, whereas shapeless particles show semiconductor properties.     

嵌入La和Gd原子的Si24笼团簇的稳定性

用梯度修正自旋极化密度泛函(DFT)电子结构计算,研究了具有Th和D2d对称性包裹La和Gd原子的Si24富勒烯的稳定性.结果表明Gd@Si24具有很高的磁性而La@Si24的磁性完全猝灭.这些结果有可能导致Si基富勒烯团簇新的结构类型.     

Structural and electronic properties of C6 cluster

First-principles total-energy calculations of structural properties of the carbon cluster C₆ have been made using the full-potential augmented plane-waves plus local orbital (APW+LO) method with the generalized gradient approximation (GGA). Initiated from a hexagonal configuration, we performed geometry optimization with damped Newton dynamics. The computed ground state atomic configuration for C₆ belongs to a monocyclic D_3h structure. The average bond length is 1.52 a.u. and the bond angle is 90.2^○, respectively, which are in agreement with the reported results.     

The influence of a cross-linking agent and C60 fullerene on the properties of a solid lubricant

The influence of a cross-linking agent, diamine, and C₆₀ fullerene on the antifriction and wear properties of a solid lubricant made of trifluorochloroethylene-vinylidene fluoride copolymer was studied for steel-to-steel sliding friction. The wear characteristics are improved in the whole range of loads investigated, while the antifriction properties, only at small loads. A qualitative wear test method is proposed in which the test-period-averaged friction coefficient of a hybrid specimen (coating plus metal substrate) is measured with a standard friction machine. A model that considers the combined interaction of the substrate and the coating with the roller was used to calculate the linear wear rate of steel and the probabilistic parameter of wear.