Electronic density of states of the cluster-Bethe-lattice and the diamond lattice with continued fraction method

The electronic density of states of diamond lattice was evaluated with the continued fraction method, up to the third and the fourth level. The result was found to be superior to the cluster-Bethe-lattice approximation to the diamond lattice.     

Electronic structure of clean and metal chemisorbed diamond (111) surfaces

The electronic density of clean and Ga-chemisorbed diamond (111) surfaces have been calculated using a cluster Bethe-lattice method. The results have been compared with those obtained for Ge (111) surfaces. A comparatively flat dangling bond band appears in both the clean and chemisorbed diamond surfaces in contrast to the other homopolar material surfaces. The metal-induced states appear on the top of the valence band as well as on the bottom of the conduction band.     

A Cluster-Bethe-Lattice approach to spin-waves in dilute ferromagnets

We study the spin-wave spectra of a dilute ferromagnet within the cluster-Bethe-lattice approximation. Short range order effects for the alloy are included. A study of finite size clusters connected at their edges to Bethe lattices of the same coordination number allows us to determine: (i) the stability condition for the magnetic system; (ii) the continuum spin-wave local density of states; and (iii) the existence of localized states below and above the continuum states.     

Spin Waves in a Surface-Diluted Quant um Spin system

A theoretical investigation of the effects of surface dilution on spin waves in a semi-infinite transverse Ising model (TIM) is presented. Within the framework of the double-time Green's function theory, the loctl density of spin-wave states is obtained by the application of the cluster-Bethe-lattice (CBL) method. Numerical calculations of paramagnetic phases reveal that surface dilution will lead to appearance of the localized spin-wave states whose frequencies are bulk independent while the corresponding density of states is a function of the exchange interactions. Increase of the bulk exchange interactions between the surface and the bulk spins tends to diminish the localized spin-wave states. Dependence of the local density of states on the concentration p of the magnetic atoms is similar with that in a three-dimensional infinite TIM which has been discussed in our previous paper.     

Magnetic Excitation at the Surface of a Substitutionally Disordered Antiferrornagnet

The magnetic excitation at the auiface of a substitutionally disordered antiferromagnet is etudied by using the Bethe-lattice method. Some numerical resulte are presented.     

New theory of binary alloys with short-range order properties

A new method for treating the electronic structure of binary alloys is presented. It is based on the study of a finite size cluster connected at its edges to a Bethe-lattice of the same coordination number. An illustrative example is presented. It includes concentration sequences which are (i) random, (ii) with a tendency to segregation and (iii) with a tendancy to form binary compounds. Energy gaps and localized states appear naturally in the method.     

Spectroscopic evidence for bonding coordination defects in amorphous as

Spectroscopic evidence for four-fold and possibly, two-fold coordinated defects in amorphous As is presented. Structure in Raman scattering and infrared absorption measurements is interpreted using force-constant models and the cluster-Bethe-lattice method. The positions and intensities of certain peaks suggest that these defects may be the analogues of valence alternation pairs in amorphous chalcogenide glasses.     

Electrons and phonons in amorphous pyramidally bonded solids

Electronic and phonon state densities of amorphous pyramidally bonded solids are calculated with As as a prototype. Using a Bethe-lattice, the Greaves-Davis random network model and the Cluster-Bethe-lattice method, the results show: (1) the phonon states are isomorphic to, and $\text{obtained}$ from, the p-like electron states, (2) the photoemission and infrared measurements are easily interpreted, and (3) the electronic and phonon state densities are $\text{extremely}$ sensitive to the local topology.     

Spatial structure of an incompressible quantum Hall strip

The incompressible quantum Hall strip is sensitive to charging of localized states in the cyclotron gap. We study the effect of localized states by a density functional approach and find electron density and the strip width as a function of the density of states in the gap. Another important effect is electron exchange. By using a model density functional which accounts for negative compressibility of the QH state, we find electron density around the strip. At large exchange, the density profile becomes nonmonotonic. Both effects, localized states and exchange, lead to a substantial increase of the strip width.     

Applications of the CPA to elemental tetrahedrally bonded amorphous semiconductors

It is pointed out that the CPA can easily be coupled with multiband, nearest-neighbor tight-binding Bethe-lattice Hamiltonians to fruitfully study the electronic structure of tetrahedrally bonded elemental amorphous semiconductors. Results are presented which illustrate the effects on the model semiconducting gap of (i) a rectangular distribution of site diagonal terms in the Hamiltonian, and (ii) vacancies distributed randomly over the lattice. The relationship of these results to experiment is briefly explored.     

硼烯纳米带能带结构和态密度的第一性原理研究

基于密度泛函理论,采用第一性原理的方法计算H修饰边缘不同宽度硼稀纳米带的电荷密度、电子能带结构、总态密度和分波态密度。结果表明,硼烯纳米带的宽度大小影响着材料的导电性能,宽度5的硼烯纳米带是间接带隙简并半导体,带隙值为0.674 eV,而宽度7的硼烯纳米带却具有金属材料的性质。分波态密度表明,宽度5的硼烯纳米带的费米能级附近主要是由B-2s、2p电子态贡献,H-1s主要贡献于下价带且具有局域性,消除了材料边缘的不稳定性。宽度7的B-2p和H-1s电子态贡献的导带和价带处于主导地位,费米能级附近B-2p和H-1s电子态的杂化效应影响材料的整体发光性能。     

An alternative approach to calculate the density of states in nonextensive statistical mechanics

A relation between the generalized partition function (Tsallis) and density of states is established by using the method of integral transform which enables reducing some integral equations into the algebraic equations. Inverse Mellin transformation of this equation gives the density of states. Similar relation is also hold the for standard partition function (Boltzmann-Gibbs) and the density of states. Using these relations, we recover the density of states for the classical ideal gas within both statistics.     

Surface segregation in CuxNi1−x alloy

The tight-bonding Hartree Hamiltonian and a mixed Bethe-lattice approximation is used to study the surface segregation phenomenon of Cu_xNi_1−x alloy. It is found that Ni atoms do segregate to the surface layer in the Cu-rich range (0.75 < x < 1). This is in contrast with previous theories which predict the enrichment of Cu atoms at the surface for all bulk Cu concentrations. However, the present theory agrees reasonably well with the recent experimental observation of a crossover at x = 0.84 by Hashizume et al. [1].     

Statistical characterization of a 1D random potential problem—With applications in score statistics of MS-based peptide sequencing

We provide a complete thermodynamic solution of a 1D hopping model in the presence of a random potential by obtaining the density of states. Since the partition function is related to the density of states by a Laplace transform, the density of states determines completely the thermodynamic behavior of the system. We have also shown that the transfer matrix technique, or the so-called dynamic programming, used to obtain the density of states in the 1D hopping model may be generalized to tackle a long-standing problem in statistical significance assessment for one of the most important proteomic tasks—peptide sequencing using tandem mass spectrometry data.     

氧化石墨烯纳米带能带结构和态密度的第一性原理研究

基于密度泛函理论,采用第一性原理方法,计算了氧化石墨烯纳米带的电荷密度、能带结构和分波态密度。结果表明,石墨烯纳米带被氧化后,转变为间接带隙半导体,带隙值为0.375 e V。电荷差分密度表明,从C原子和H原子到O原子之间有电荷的转移。分波态密度显示,在导带和价带中C-2s、2p,O-2p,H-1s电子态之间存在强烈的杂化效应。在费米能级附近,O-2p态电子局域效应的贡献明显,对于改善氧化石墨烯纳米带的半导体发光效应起到了主要作用。     

Two-dimensional Green tensor and local density of states in finite-sized two-dimensional photonic crystals

The two-dimensional Green tensor for two-dimensional photonic crystals, consisting of clusters of circular cylinders of infinite length, is constructed using the exact theory of multipole expansions. On the basis of this Green tensor, the local density of states for both polarizations is calculated, showing how the density of states depends on the position inside the crystal. We include results for clusters with a waveguide, obtained by removing a line of cylinders, and a cavity, obtained by forming a localized defect.     

Density of vibrational states of a hyperquenched glass

The vibrational density of states of a hyperquenched and an annealed glass has been measured using nuclear inelastic scattering. The hyperquenched sample shows a higher number of vibrational states in the low-energy region with respect to the annealed glass. It reveals, however, lower density and sound velocity and, therefore, smaller Debye energy. After rescaling the energy axes in Debye energy units and area renormalization, the density of states of both samples becomes identical. Thus, the effect of quenching is described by the transformation of the continuous medium.     

Effect of nonmagnetic impurities on the critical temperature of the itinerant-electron antiferromagnet

The effect of nonmagnetic impurities on the critical temperature of the itinerant-electron antiferromagnet is investigated using a Fedders-Martin model with an energy dependent density of states.It is found that nonmagnetic impurities can increase the critical temperature T_N if the density of states is changed by the impurities. This result is in agreement with the experimental results for CrRu alloys.     

Direct determination of vibrational density of states change on ligand binding to a protein

The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium.     

Electronic structure of the SiAu surface

The electronic density of states of the SiAu surface is calculated using a continued fraction technique. The geometric structure of the surface alloy Au₄Si is generated by molecular dynamics. The local density of states on Si atoms in a metallic environment differs qualitatively from the sp spectrum of a typical semiconductor. The calculated densities of p states of Si are in good agreement with recent X-ray spectra of Si in a metallic environment.