Energy of bonding an adsorbed atom with a single-layer graphene

The change in the local density of states δρ _g of a single-sheet graphene due to adsorption of a single atom has been calculated in the framework of the M model proposed earlier. The dependence of the local density of states δρ _g on the position of the adatom energy level ɛ _a with respect to the Dirac point and other parameters of the problem has been analyzed. It has been shown that the largest changes in the local density of states δρ _g are caused by adatoms with the ɛ _a levels lying in the vicinity of the Dirac point, so that the minimum density of states of graphene remains equal to zero. An analytical expression has been derived for the energy of bonding W _ads of the adatom with graphene. The obtained estimates of the bonding energy W _ads in the weak and strong adatom-substrate bonding regimes are presented. Atoms of alkali metals and halogens have been considered as specific adsorbates.     

石墨带的晶格动力学研究

基于晶格动力学理论,采用力常数模型,计算了石墨带的声子色散关系、振动模式密度和比热.计算结果表明,石墨带的声子谱特征介于一维碳纳米管和二维石墨片之间.扶手椅型和锯齿型石墨带的中、高频声子支分别与锯齿型和扶手椅型碳纳米管的类似.由于声子限域效应,低频声子支随着石墨带带宽的改变出现明显的频移现象.振动模式密度在高频区几乎不敏感于带宽,而低频区的峰位随着带宽的增加而逐渐向低频移动.此外,无论是在低温还是高温,比热都随着带宽的增加而逐渐降低,呈现量子尺寸效应.在300K时,比热可以拟合成C_V=C_Vg+A/n,其中C_Vg为石墨片的热容,而A/n项反映了石墨带中边缘效应对比热的影响. 关键词： 石墨带 声子色散关系 比热     

Transition metal and rare-earth metal atoms on single-layer graphene: Estimations of the charge transfer and adsorption energy

A Hamiltonian accounting for s- and d(f)-states of adatoms has been proposed to describe adsorption of atoms of d- and f-metals on single-sheet graphene. It has been shown that s-electrons mainly contribute to the charge transfer Δn _a between the adatom and graphene substrate. Analytical formulas proposed previously within the M-model of the graphene density of states are used for Δn _a calculations. To estimate the adsorption energy, a simple analytical expression is proposed. Calculations are performed for 3d-, 4d-, 5d-, and 4f-adatoms. The results of calculations are compared with the data obtained by other authors.     

Band-structure properties of photonic superlattices

The band structure of a one-dimensional periodic array composed of two different layers of dimensions a and b characterized by refractive indices n ₁ and n ₂, respectively, is investigated. Refractive indices may take on positive as well as negative values. Within the Maxwell framework and using a transfer matrix technique for one dimensional periodic eigen-problems, we have determined a general equation, which governs the photonic band structure and the density of states (DOS) of one-dimensional photonic crystals. In addition to the well-known existence of the band gaps, we show that, depending on the width relationship b/a between the layer materials, super-lattices with null photonic band gap may exist and the conditions for such occurrences are established. Furthermore, we have been able to study the so-called 〈n〉 = 0 non-Bragg gap, ground ω₀, for which the average refraction felt by the propagating radiation is null. The text was submitted by the authors in English.     

氦对LaNi5晶体结构的影响及其扩散特性研究

从密度泛函理论为基础的第一性原理出发,运用全势能线性缀加平面波(FLAPW)方法,对氚衰变后氦在合金中的占位以及LaNi₅He晶体结构进行了理论计算,并系统给出了氦在间隙间的迁移曲线.结果表明,氦原子在十二面体(1b)格位最稳定,并且氦从6m格位向1b格位迁移不存在势垒,而从2d格位向1b格位迁移则需越过1.55eV高的势垒.另外,氦从12n格位穿过12o格位最后到达6m格位也无明显势垒存在,并且处于4h格位之间的氦原子可以自由迁移,而相应12n格位之间的直接迁移则需跨越13.6eV高的势垒.最后还计算给出了氚衰变后合金的态密度、电子密度以及势能分布图,并与相应的LaNi₅H结构作了详细比较. 关键词： 全势能线性缀加平面波(FLAPW) 5He')" href="#">LaNi₅He 态密度 扩散     

Non-partial-wave Coulomb-Born theory for the excitation of many-electron atomic ions II: Numerical description and application

A non-partial-wave Coulomb-Born theory is recently formulated to treat the excitation of many-electron atomic ions for impact by an arbitrary charged particle [Y.B. Duan et al., Phys. Rev. A 56, 2431 (1997)]. The multiple expansion of the transition matrix element is decomposed into the target form factor and the projectile form factor. These are the matrix elements of the tensor operators between quantum states so that any complicated wave function for the target ion can be employed. In this formal theory, an infinitesimally small positive quantity is introduced artificially to guarantee the convergence of integrals. As a supplementary part of the theory, we discuss how to choose the value of . It is found that the should be taken as functions of the momentum transfer and multipolarity . Illustrations are carried out by calculating the cross-sections for some typical transitions n _a l _a -n _b l _b of hydrogen-like ions for impact by electron, positron, and proton, respectively. The resulting cross-sections are in good agreement with ones produced by using a method available for ion targets with Slater-type orbitals [N.C. Deb, N.C. Sil, Phys. Rev. A 28, 2806 (1993)]. Comparisons demonstrate that the Coulomb-Born theory with non-partial wave analysis provides a powerful method to treat the excitation of many-electron atomic ions impact by an arbitrary charged particle. Received 6 April 1999     

Resonance optical spectroscopy of long-period quantum-well structures

Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well, n _a, and barrier-material refractive index nb. General expressions for the optical reflection and transmission coefficients for a structure with N equidistant quantum wells are derived with the use of the Green’s function and transfer matrix methods. Normal and oblique light reflectance spectra from II-VI-based heterostructures were found to reveal a bright interference pattern caused by the difference between n _a and n _b. A comparison of the theory with experiment has yielded the dispersion of n _a and n _b within a broad wavelength range and the parameters of the quasi-two-dimensional heavyhole exciton (e1-hh1), namely, the resonant frequency and the radiative and nonradiative damping rates. Reflectance spectra from resonant Bragg and quasi-Bragg structures with real exciton parameters are calculated, and the effect on these spectra of the refractive-index difference and the deviation from the Bragg condition is analyzed. Fiz. Tverd. Tela (St. Petersburg) 39, 2072–2078 (November 1997)     

The one-dimensional 1/4-filled Hubbard model with alternating interactions

The one-dimensional Hubbard model with different on-site interaction on the even (U_a) and odd (U_b) sites is considered within the framework of the weak coupling approach. In the case of a 1/4-filled band the dynamical nonequivalence of sites leads to the appearance of Umklapp processes in the system and to the dynamical generation of a commensurability gap in the charge excitation spectrum for U_a ≠ U_b and U_a>0 or U_b>0. Depending on the relation between the bare coupling constants the system shows four different regimes of behaviour in the infrared limit corresponding to normal metal, nonmagnetic insulator, antiferromagnetic insulator and superconducting states. The extended model including interaction between particles on nearest and next-nearest neighbour sites is also considered.     

增加光子对和减少光子对相干态的统计性质

引入增加光子对相干态|ζ,q;m >_a=a^+m|ζ,q >和减少光子对相干态|ζ,q;-m >_b=b^m|ζ,q >,研究了这些态所描写的光场的统计性质。结果显示当在对相干态的a模增加光子时,两模的平均光子数均增加,亚泊松分布性质增强;当在对相干态的b模取走光子时,b模的平均光子数减少,而a模的平均光子数却增加;b模的亚泊松分布性质减弱,而a模的亚泊松分布性质却增强。我们还计算了场模间的相关度和场模的压缩。     

Structural and electronic properties of InNxP1-x alloy in full range (0 ≤ x ≤1)

We have performed first-principles method to investigate structural and electronic properties of InN_xP_1?x ternary semiconductor alloy in full range (0 ≤ x ≤ 1) using density functional theory. We have used modified Becke–Johnson potential to obtain accurate band gap results. From the electronic band structure calculation we have found that InN_xP_1?x become metal between 47 and 80% of nitrogen concentration. Additional to our band gap calculations, we have also used the band anticrossing model. The band anticrossing model supplies a simple, analytical expression to calculate the physical properties, such as the electronic and optical properties, of III-N_xV_1?x alloys. The knowledge of the electron density of states is required to understand and clarify some properties of materials such as the band structures, bonding character and dielectric function. In order to have a deeper understanding of these properties of the studied materials, the total and partial density of states has been calculated. Finally, we have calculated the total bowing parameter b of studied alloys, together with three contributions b_VD, b_CE, and b_SR due to volume deformation, different atomic electron negativities and structural relaxation, respectively.     

Adiabatic Hyperspherical Approach to the Problems of Muon Catalyzed Fusion

The adiabatic hyperspherical approach (AHSA) is applied for the numerical investigation of the scattering processes and resonances in Coulomb three-body mesic atomic systems. The results of the calculations of elastic and inelastic cross sections in low-energy collisions aμ + b (a, b = p, d, t), energies, lifetimes and local characteristics of resonant states of mesic molecular ions ⁿ Heaμ⁺ (n = 3, 4) are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

类氖等电子系列离子基态的双电子复合速率系数研究

使用全相对论组态相互作用方法, 能级-能级细致计算了0.1 E_I ≤ kT_e≤ 10 E_I (E_I是类钠离子基态的第一电离能) 温度范围内类氖离子基态双电子复合(DR)速率系数, 双激发自电离能级考虑了(2s2p)⁷3ln'l', (2s2p)⁷4l4l' 以及(2s2p)⁷4l5l'组态. 对于(2s2p)⁷3ln'l'双激发自电离组态, 轨道角量子数l' >8 的(2s2p)⁷3ln'l'双激发自电离态对双电子复合速率系数的贡献可以忽略不计; (2s2p)⁷3ln'l'双激发自电离组态的高里德堡态对双电子复合速率系数的贡献满足 n'^-3组态-组态外推法, 并且核电荷数越大, 趋于n'^-3标度的n'值越小; 对细致能级计算得到的类氖离子基态的总DR速率系数进行了拟合, 得到类氖离子基态的总DR速率系数随核电荷数 Z和电子温度变化的经验公式, 该拟合公式与细致计算结果的偏差在2%以内, 能较准确的计算任意核电荷数Z的类氖离子在0.1E_I ≤ kT_e ≤ 10E_I电子温度范围的DR速率系数. Burgess-Merts(BM)近似公式不适用于估算低温(kT_e<0.3 E_I)类氖离子的DR速率系数, 在高温(kT_e>2E_I)时, 类氖离子的DR速率系数可以用BM近似公式表示.     

Energy bands and electron densities of Li3N

Self-consistent band-structure calculations on the fast ionic conductor lithium nitride are performed by means of the linearized augmented plane wave (LAPW) method within the local density formalism. The corresponding density of states is decomposed into local (inside spheres), partial (l-like) and symmetry (p _x p _y ;p _z ) components from which an only very small covalent contribution to the bonding in Li₃N can be deduced. Electron density maps reveal Li₃N to be highly ionic (near Li⁺ and N^3–). A simple Watson model, although a good first approximation, cannot account for all details. For instance a remarkable non-spherical electrons density is found around N which may explain the high electric field gradient experimentally observed on this site; furthermore a reduced electron density around the Li-sites appears in contrast to a simple supper-possition of N^3– ionic densities. However, calculated x-ray structure factors and difference electron densities are in good qualitative agreement with recent x-ray diffraction experiments.This work has been supported by the Hochschuljubiläumsstiftung der Stadt Wien. All calculations were carried out at the Rechenzentrum der Technischen Universität Wien     

Si在TiAl3中取代行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl₃中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl₃中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl₃中松散分布的Al（2）原子.对c/a值的计算表明,随Al（2）格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al（1）格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl₃中的极限固溶度介于12.5at%—18.75at%之间. 关键词： 密度泛函理论 第一性原理 电子结构 3')" href="#">TiAl₃     

IR spectrum and localization of excitation of reaction center of photosystem II in triplet state

Using the density functional theory, vibrations of different model forms of the chlorophyll a molecule in the ground and triplet states have been calculated. The assignment of the experimental difference IR spectrum corresponding to the formation of the triplet state of the photosynthetic reaction center of photosystem II has been proposed on this basis. It has been shown that molecules of accessory chlorophyll B _A and B _B located between the special pair and H _A and H _B pheophytin molecules can be involved in the intermolecular hydrogen bond with the water molecule. The energy of this interaction in the triplet state of molecules for B _A is larger on 6 kcal/mol. This allows us to relate this pigment to the location of the triplet excitation at the reaction center of photosystem II.     

Inverse resonance scattering for Jacobi operators

The Jacobi operator (Jf) _n = a _n−1 f _n−1 +a _n f _n+1 + b _n f _n on ℤ with real finitely supported sequences (a _n − 1) _n∈ℤ and (b _n ) _n∈ℤ is considered. The inverse problem for two mappings (including their characterization): (a _n , b _n , n ∈ ℤ) → {the zeros of the reflection coefficient} and (a _n , b _n , n ∈ ℤ) → {the eigenvalues and the resonances} is solved. All Jacobi operators with the same eigenvalues and resonances are also described.     

The role of the covalent interaction in the formation of the electronic structure of Au- and Cu-intercalated graphene on Ni(111)

A study is reported of the role played by covalent interaction in the coupling of graphene formed on Ni(111) to the Ni substrate and after intercalation of Au and Cu monolayers underneath the graphene. Covalent interaction of the graphene π states with d states of the underlying metal (Ni, Au, Cu) has been shown to bring about noticeable distortion of the dispersion relations of the graphene electronic π states in the region of crossing with d states, which can be described in terms of avoided-crossing effects and formation of bonding and antibonding d-π states. The overall graphene coupling to a substrate is mediated by the energy and occupation of the hybridized states involved. Because graphene formed directly on the Ni(111) surface has only bonding-type occupied states, the coupling to the substrate is very strong. Interaction with intercalated Au and Cu layers makes occupation of states of the antibonding and bonding types comparable, which translates into a weak resultant overall coupling of graphene to the substrate. As a result, after intercalation of Au atoms, the electronic structure becomes similar to that of quasi-free-standing graphene, with linear dispersion of π states at the K point of the Brillouin zone and the Dirac point localized close to the Fermi level. Intercalation of Cu atoms under the graphene monolayer results, besides generation of covalent interaction, in a slight charge transport, with a partial occupation of the previously unoccupied π* states and the Dirac point shifted by 0.35 eV toward increasing binding energy.     

Relaxation times for establishing steady state populations in optically thin helium plasmas

Population densities of HeI and HeII excited states are calculated from a collisional radiative model for non-LTE optically thin helium plasmas. Effect of direct ionisation-excitation of HeI to HeII states on the population density of HeII states is shown. Relaxation times for HeI states calculated from the CR model is reported forT _e from 3 to 18 eV andn _e from 10⁹ to 10¹⁶ cm⁻³. Part of a research project supported by the Department of Atomic Energy.     

Spin-polarized Dirac-Slater calculations on the energies of hollow argon atom

In this work, the multiplet splitting in terms of a spin-dependent model is analyzed. The spin-polarized and unpolarized single configuration Dirac-Fock-Slater wavefunctions have been used in the evaluation of the total energies of highly ionized argon with different L shell population The transition energies of hollow argon atom with initial configurations 1s ⁰ _1/22s ^m _1/22p ⁿ _1/22p ^l _3/2 with m = 0 to 2 and n + l varying from 6 to 1 are reported in this work. The calculations have been carried out by taking into account a relativistic exchange potential in the Dirac-Slater potential. To account for the correlation effects, a correction term has also been considered perturbatively. The present calculations show that the spin-polarized technique which is mainly applied to the ground states of atoms may also be applied to atoms ionized in the inner shells with a good degree of accuracy. Received 5 December 2000 and Received in final form 9 April 2001     

Class two analogue of T. Y. Thomas's theorem and different types of embeddings of static spherically symmetric space-times

A Riemannian space of embedding class two is characterised by two symmetric tensors a _ij , b _ij and a vector s_i, satisfying the equations of Gauss, Codazzi and Ricci. It is proved that the Gauss equations together with one set of Codazzi equations imply the other set of Codazzi equations and the Ricci equations, provided that the matrix of the tensor b _ij (or a _ij ) is nonsingular. (The class m generalisation of the result has also been suggested). The result so proved has further been utilized in finding explicitly the a _ij 's and b _ij 's in the case of the static spherically symmetric line element. It is further indicated that the a _ij 's and b _ij 's so obtained are responsible for the different types of embeddings of the spacetime considered.