Effect of correlation and spin-polarisation on the band structure of metallic dysprosium

Energy bands of dysprosium have been calculated considering the effects of correlation and spin-polarisation. The exchange and correlation contributions to the spherically symmetric crystalline potential have been taken in the forms suggested by (i) Kohn and Sham and (ii) Overhauser. The exchange and correlation potential of von Barth and Hedin has been used to study the effect of spin-polarisation on the band structures. The resulting bandwidth, density of states, magnetic moment and spin-splitting have been computed and compared with experimental results. Some discrepancies remain; theoretical calculations done so far agree reasonably among themselves, so accurate experimental data are probably called for.     

Exchange and correlation interactions and band structure of non-close-packed solids

The electronic properties of solids are calculated by the Green’s function method taking account of the deformation of the atomic spheres to atomic ellipsoids by the crystal field. It is shown that the ratio of the correlation and exchange interactions in the crystal influences the nature of the band structure in non-close-packed solids. Fiz. Tverd. Tela (St. Petersburg) 40, 1990–1994 (November 1998)     

Susceptibility — Knight shift correlation and the band structure of VO2

The magnetic susceptibility and⁵¹V Knight shift have been measured in powdered VO₂ from the semiconductor-metal transition temperatureT _t=341°K to 478°K. The fact that both depend linearly on temperature enables the orbital and spin contributions to both quantities to be evaluated. The orbital and spin susceptibilities at 341°K are found to be 1.30±0.07 and 7.49±0.07μemu g^?1, respectively, and the corresponding shifts +0.61±0.04% and ?1.00±0.04%. The existence and magnitude of the orbital term are consistent with the currently accepted two band model of VO₂ aboveT _t.     

Effect of the band structure on the thermoelectric properties of a semiconductor

The dependence of the thermoelectric parameters of a material on the band position and carrier effective masses is studied theoretically. The optimum parameters providing an increase in the thermoelectric figure-of-merit are specified. The results obtained are applied to the n-type Mg₂Si-Mg₂Sn solid solutions, in which the complex structure of the conduction band is one of the factors responsible for an increase in the thermoelectric efficiency.     

界面耦合对共聚物能带及键结构的影响

建立了紧束缚近似下的二嵌段共聚物-(A)x-(B)y-的物理模型,研究了组成共聚物的均聚物间界面相互作用-界面耦合的强弱对共聚体系的能带结构、键结构性质等的影响.共聚物的带隙也可通过改变均聚物之间的界面相互作用来加以调制,进一步发现可用界面势阱或能垒(energy barrier)来表征界面耦合的强弱.     

Effect of band structure on quantum interference in multiwall carbon nanotubes

We report conductance measurements on multiwall carbon nanotubes in a perpendicular magnetic field. A gate electrode with large capacitance is used to considerably vary the nanotube Fermi level. This enables us to search for signatures of the unique electronic band structure of the nanotubes in the regime of diffusive quantum transport. We find an unusual quenching of the magnetoconductance and the zero bias anomaly in the differential conductance at certain gate voltages, which can be linked to the onset of quasi-one-dimensional subbands.     

面心立方金属铈的高压电子结构研究

本文简要介绍了我们开发的基于密度泛函理论和动力学平均场理论(DFT+DMFT)的全自洽的的计算程序,并运用该程序研究了面心立方金属铈的等结构相变.动力学平均场采用的是目前公认的最为准确和高效的连续时间蒙特卡罗方法作为杂质求解器.我们首先分别计算了γ和α相的电子态密度,该结果可以正确的描述两个相的电子结构特征.然后计算了不同温度下的相变前后的电子结构,从中可以得到电子结构在不同温度下的相变过程,与之前的实验结果一致.这一工作为以后进一步的金属铈的等结构相变研究打下了基础.     

面心立方金属铈的高压电子结构研究

本文简要介绍了我们开发的基于密度泛函理论和动力学平均场理论（DFT+DMFT）的全自洽的的计算程序,并运用该程序研究了面心立方金属铈的等结构相变. 动力学平均场采用的是目前公认的最为准确和高效的连续时间蒙特卡罗方法作为杂质求解器. 我们首先分别计算了 和 相的电子态密度,该结果可以正确的描述两个相的电子结构特征. 然后计算了不同温度下的相变前后的电子结构,从中可以得到电子结构在不同温度下的相变过程,与之前的实验结果一致. 这一工作为以后进一步的金属铈的等结构相变研究打下了基础.     

Fermi surface and band mapping of the cerium/palladium surface alloy

X-ray and UV excitation angle-resolved photoemission spectroscopy of ultra-thin films of cerium deposited on Pd(1 1 1) single-crystal surface has been carried out. Photoelectron diffraction pattern showed that deposition of 1 ML of Ce led to a formation of Ce-Pd substitutional alloy. Valence band spectra measured with high angular resolution permitted to plot valence band maps and Fermi surface scans and showed formation of surface alloy exhibiting d- and f-electron orbital hybridization. A shift of Pd 4d-derived states to higher binding energy in the Ce-Pd systems was observed.     

Effect of overlap of localized orbitals on the band structure of insulators under pressure

A new method for calculating the energy spectra of compressed insulators based on the cluster expansion is proposed. The dependence on the compression of the spectra of both the conduction band and the valence bands is uniquely determined by the values of the overlap integrals of the orbitals of pairs of isolated atoms. The overlap integrals and the matrices defined by them are calculated numerically for inert-gas crystals and their properties and values are analyzed for different lattice constants. Numerical calculations of the bands of the compressed crystal in the various proposed models are carried out and discussed for neon. Fiz. Tverd. Tela (St. Petersburg) 40, 1464–1472 (August 1998)     

Magnetic band structure in the valence band of CdSb

Starting from the band structure calculations of Yamada, we have undertaken to calculate in analytic form the Landau levels, de Haas-Shubnikov oscillation periods and effective masses in the valence band of CdSb. Because of the anomalous character of the E — k relation in the x-direction, it is necessaryto use different approximation methods for low and high hole energies; between the two is a region for which calculation is very difficult. Analytic forms have been obtained in both regimes, which should facilitate the calculation of magneto-transport properties and thus the determination of band parameters.     

Effect of metal and carbon vacancies on the band structure of hexagonal tungsten carbide

The band structure of hexagonal tungsten carbide (β-WC) containing vacancies in metal and carbon sublattices is investigated within the first-principles full-potential linear muffin-tin orbital (LMTO) approach for a model of 16-atom supercells. Specific features of the formation of “vacancy” states are discussed, and the formation energies of defects and their charge states are estimated. The results obtained are compared with previous calculations and available experimental data.     

Electronic structure of cerium once more

Recent measurements of the inelastic scattering of γ-rays (the Compton profile) in the γ- and α-phases of cerium are interpreted in terms of a simple model. Our interpretation is inconsistent with the promotion model, but supports the idea that the γ ? α transition is due to electron correlation with essentially no change of the 4?-occupancy. The Mott, Anderson and spin-polarised band structure models are discussed.     

Electronic structure of cerium heavy-fermion systems

A number of cerium-based systems are investigated using x-ray photoelectron spectroscopy. It is revealed that there is a correlation between the parameters of the x-ray photoelectron spectra and the heavy-fermion state. This correlation makes it possible to investigate the relaxation processes, anomalously strong reorganization of orbitals, profound collective effects induced by a vacancy field, and hybridization of localized unoccupied f states with delocalized occupied states.     

Effect of the d-f correlation on the electronic structure of intermediate valence systems

The electronic structure of an intermediate valence system is calculated by means of a real space renormalization technique on a Bethe lattice. The d-f Coulomb repulsion G is treated into the alloy analogy approximation. The valence and the densities of states are calculated as a function of G. We find that the hybridization gap decreases when G increases, and that the density of states at the Fermi level exhibits a peak as a function of G.     

Effect of interdiffusion on the band structure and absorption coefficient of a one-dimensional semiconductor superlattice

The effect of interdiffusion of Al and Ga atoms on the confining potential, band structure and absorption coefficient of electromagnetic radiation of a one-dimensional superlattice, composed of GaAs/Ga_1?x Al _x As quantum wells with the initially rectangular potential profile, is studied within the framework of the modified Wood-Saxon potential model. It is shown that the interdiffusion leads to the widening of the energy minibands and to the blueshift of the absorption spectrum observed in experiments.     

N掺杂对zigzag型石墨烯纳米带的能带结构和输运性质的影响

用第一性原理研究了N掺杂zigzag型石墨烯纳米带(z-GNRs)的能带结构、透射谱和电流电压特性,研究结果表明N掺杂将使得z-GNRs的能带结构中出现能隙,材料从金属转变为半导体;随着杂质浓度的增大,相同偏压下电流明显减小,同时体系费米面附近的透射率逐渐减小;z-GNRs的长度、宽度以及N原子的替代掺杂位置均会对输运性质产生影响,在宽度较小的情况下,掺杂浓度和掺杂位置两种因素共同影响体系的输运性质. 关键词： 石墨烯纳米带 N掺杂 能带结构 输运性质