GaAs和AlAs光学声子形变势的第一性原理研究

本文以冻结声子近似模型,采用空球随原子球位移的冻结势近似的LMTO-ASA计算方案,研究了GaAs和AlAs布里渊区Λ轴的光学声子形变势的计算,得到Γ点和Λ轴光学声子形变势d₀,d₃₀,d₁₀(val)和d₁₀(comd)的第一性原理的计算结果。研究中着重从GaAs和AlAs的Λ轴光学声子形变势随k点的变化趋势,从光学声子形变势在Γ点附近满足的关系,以及从不同计算方法对d₀的计算结果与实验结果的比 关键词：     

Ⅲ-V族化合物半导体Λ轴光学声子形变势的研究

本文在LMTO-ASA能带计算中,采用冻结声子模型,系统地研究了Ⅲ-V族化合物半导体的Λ轴光学声子形变势随k值的变化关系,提供了9种Ⅲ-V族化合物在Λ轴不同k值情况下的光学声子形变势d₃₀(Λ), d₁₀(Λ,val)和d₁₀(Λ,con)的第一原理计算结果。     

Ga1-xAlxAs光学声子形变势研究

本文用LMTO-ASA能带技术结合新的虚晶近似处理方法和冻结声子模型,计算了三元合金Ga_1-xAl_xAs Γ点的光学声子形变势(ODP)do及A轴上ODP的d₃₀,d₁₀(val)和d₁₀(cond),预言了它们作为Al组分x的函数关系,发现这些ODP都可用x的二次方程表示,其中d₀随x增加而减小的弯曲参数很小,是近乎线性的,理论预言了x≈0.65处d₁₀关键词：     

A theoretical deduction of the shape and size of nanocarbons suitable for hydrogen storage

We evaluated the adsorption energy of a hydrogen molecule in nanocarbons consisting of graphene sheets. The nanocarbon shapes were a pair of disks with separation 2d, a cylinder with radius d, and a truncated sphere with radius d. We obtained the adsorption energy in the form of a 10–4 Lennard–Jones function with respect to 1/d. The values of the potential depth (D) and equilibrium distance (d _e), respectively, were 94 meV and 2.89 Å for the disk pair, 158 meV and 3.14 Å for the cylinder, and 203 meV and 3.37 Å for the sphere. When d=d _e, the adsorption energy of the disk pair (cylinder) became deeper than ?0.9D, and it approached ?D when the radius (length) increased to more than twice its separation (radius). The adsorption energy of the sphere was increased from ?D to ?0.5D when the radius of the opening increased from 0 to d _e. These results suggest that porous carbon materials can increase the adsorption energy by up to ～200 meV if the carbon atoms are arranged on a spherical-like surface with ～7 Å separation. This may lead to practical hydrogen storage for fuel cells.     

Beobachtung der inneren Paarbildung an200Hg nach Neutroneneinfang

Absolute excitation functions and angular distributions have been measured for the reactions⁹Be(d, p₀),⁹Be(d, p₁),⁹Be(d, t₀),⁹Be(d, α₀) and⁹Be(d, α₁) at energies between 0.6 and 2.7 MeV. Attempts to fit some of the data with DWBA calculations are discussed.     

A1 g phonons in YBa2Cu3O7 by first-principles atomic-force calculations

We report on ab-initio frozen-phonon calculations for the five A_1g Raman-active-modes of YBa₂Cu₃O₇ atq=0. The determination of the equilibrium positions of the atoms Ba, Cu(2), O(2), O(3), O(4) as well as of phonon frequencies and respective eigenvectors is based on the calculation of atomic forces within the LAPW-method. The general agreement between our results and experimental structural data and phonon frequencies is good. Deviations are discussed in connection with the local-density approximation.     

Study of the electronic structure of rhenium and tungsten oxides on the O K-edge

Oxygen K-edge x-ray absorption spectra were studied on the electrochromic amorphous thin film a-WO₃ in the comparison with crystalline oxides having variable electronic (d⁰, d¹, d²) and atomic structure: monoclinic m-WO₃ (insulator - d⁰), cubic Na_0.6WO₃ (metal - d¹), cubic ReO₃ (metal - d¹), layered-type hexagonal h-WO₃, WO₃H₂O and with intercalated H_xReO₃ (metal - d²), H_xWO₃ oxides having a metal-isulating transition. The changes in the XANES range 10–15 eV above the absorption edge are interpreted based on the known band-structure calculations. The high-energy features are related to the multiple-scattering processes (EXAFS) on the nearest atoms. The intensity of the feature at 550–560 eV is attributed for the first time to the value of the metal-oxygen-metal bond angle. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Deuteron d-state effects for the reactions 117Sn(d, p)118Sn and 119Sn(d, p)120Sn

Angular distributions of the differential cross section and the three tensor analyzing powers were measured for the reactions ¹¹⁷Sn($\text{d}$, p)¹¹⁸Sn and ¹¹⁹Sn($\text{d}$, p)¹²⁰Sn at E_d = 12 MeV. In addition, excitation functions of the tensor analyzing power T₂₀ were measured at proton lab angles of 0° and 5° for energies ranging from 10 to 12 MeV. At forward angles, the tensor analyzing powers for the ground state (l_n = 0) transitions are more than an order of magnitude larger than the predictions of distorted-wave calculations which neglect the deuteron D-state. Qualitative agreement with the measurements is obtained when the D-state is included.     

Islands of stability of the d-wave order parameter in s-wave anisotropic superconductors

In this paper we find and present on diagrams in the coordinates of η=2t₁/t₀ (the ratio of the second and the first nearest neighbor hopping integrals) and n (the carrier concentration) the areas of stability for the superconducting spin-singlet s- and d-wave and the spin-triplet p-wave order parameters hatching out during the phase transition from the normal to the superconducting phase. The diagrams are obtained for an anisotropic two-dimensional superconducting system with a relatively wide partially-filled conduction band. We study a tight-binding model with an attractive nearest neighbor interaction with the amplitude V₁, and the on-site interaction (with the amplitude V₀) taken either as repulsive or attractive. The problem of the coexistence of the s-, p- and d-wave order parameters is addressed and solved for chosen values of the ratio V₀/V₁. A possible island of stability of the d-wave order parameter in the s-wave order parameter environment for a relatively strong on-site interaction is revealed. The triple points, around which the s-, d-, and p-wave order parameters coexist, are localized on diagrams. It is shown that results of the calculations performed for the two-dimensional tight-binding band model are dissimilar with some obtained within the BCS-type approximation.     

Numerical study on flame spread of an n-decane droplet array in different temperature environment under microgravity

A series of numerical calculations of flame spread of an n-decane droplet array was conducted at different ambient temperatures (T_a = 300 and 573 K) for S/d₀ from 1.5 to 10, where S is the droplet interval and d₀ is the initial droplet diameter. The authors compared these numerical results with experimental results under similar conditions at different ambient temperatures for the first time in this study. Good qualitative agreement in flame spread behavior between numerical results and microgravity experiments is obtained. Flame spread mode changed with an increase in S/d₀. Also, appearance of the flame spread mode in a stepping-stone manner (Mode III in [Jpn. Soc. Mech. Eng. 68 (672) (2002) 2423]) in a normal temperature environment was verified by numerical calculations and microgravity experiments, although it was not predicted in the theoretical analysis. In addition, good qualitative agreement of flame spread rate V_f versus S/d₀ was obtained between numerical and experimental results, although numerical results were at least twice as large as experimental results. V_f had a maximum peak at a specific S/d₀ for a different ambient temperature. Employment of improved reaction model and consideration for thermal radiation heat transfer are expected to produce quantitatively better results. An increase in surface temperature of unburned droplets and the development of a flammable gas layer around the droplets were promoted in a high-temperature environment, due to an increase in heat transfer from ambient air to the droplet. As a result, V_f was increased by the higher ambient temperature, suggesting that ambient temperature plays a significant role both in the flame spread mode and the flame spread rate through promotion of a flammable gas layer around unburned droplets.     

Spectator and participator processes in the resonant photon-in and photon-out spectra at the Ce L3 edge of CeO2

We study both theoretically and experimentally the photon-in and photon-out spectra of CeO₂, which are caused by the Ce 2p to Ce 5d excitation followed by the three different de-excitation channels: (i) Ce 3d to Ce 2p (denoted by 3d-RXES), (ii) O 2p to Ce 2p (v-RXES), and (iii) Ce 5d to Ce 2p (RIXS). In 3d- and v-RXES, the 5d electron plays a role of a spectator, but in RIXS it is a participator. By extending our single impurity Anderson model (SIAM), which was used recently for our calculations of v- and 3d-RXES spectra of CeO₂, we study the polarization dependence in the spectator and participator spectra, and we perform more detailed calculations for 3d- and v-RXES spectral features, as well as new calculations for the RIXS spectrum with charge transfer excitations. The polarization dependence is different for the spectator and participator spectra; we have no polarization correlation between the incident and emitted photons for the spectator spectra but a strong polarization correlation for the participator spectrum. The theoretical calculations predict that the charge transfer excitations in RIXS occur in the transfer-energy range overlapped with v-RXES, but the RIXS and v-RXES spectra can be discriminated by taking advantage of the different polarization dependence. The overlapped RIXS and v-RXES spectra are observed successfully by our experiments and well reproduced by our SIAM calculations.     

Determination of the primary dose component and primary linear attenuation coefficient in a 6 MV photon beam using a small attenuator

It is a common technique in radiotherapy treatment planning systems to simplify the calculations by splitting the radiation beam into two components: namely the primary and scattered components. The contributions of the two components are evaluated separately and then summed to give the dose at the point of interest.Usually the primary dose is obtained experimentally by extrapolating the ionization measured within the medium to zero-field size (Godden, 1983). This approach offers the opportunity to obtain the primary component of dose without the need for a non-linear extrapolation. It is based on a paper by Nizin and Kase from 1988.The primary dose can be obtained from four measurements of ionization in narrow beam geometry and two measurements of ionization in a large beam in a phantom. If these measurements are performed over a range of different depths, the primary linear attenuation coefficient can also be obtained.The value for the primary dose at d_max in a 10 cm × 10 cm field obtained in a 6 MV beam using this method is D_p(d_max, 10 cm × 10 cm) = 0.925 Gy/100 MU for a 1 cm thick lead attenuator and is D_p(d_max, 10 cm × 10 cm) = 0.941 Gy/100 MU for a 2 cm thick lead attenuator. The primary linear attenuation coefficient is μ₀ = 0.0445 ± 0.0007 cm^?1.The obtained values of the primary dose component compare well with the extrapolation of the phantom scatter correction factor to zero-field size from measurements done in the same beam and also to literature (Rice and Chin, 1990). One can thus conclude that this method has the potential to provide an independent measurable verification of calculations of primary dose.     

Theoretical investigation of the intrinsic piezoelectric properties for tetragonal BaTiO3 epitaxial films

The orientation dependences of the converse longitudinal piezoelectric constant d_33,f, and the in-plane converse piezoelectric constant e_31,f, are calculated for tetragonal barium titanate epitaxial films. The calculations demonstrate that both e_31,f and d_33,f have their maximum values along an axis close to the (1 1 1) direction of the pseudo-cubic system, which are similar to the orientation dependence results for a tetragonal BaTiO₃ single crystal. The calculated piezoelectric constants for a (1 1 1) oriented BaTiO₃ epitaxial film (e_31,f = −23 C/m², d_33,f = 124 pm/V) suggest that it is a good candidate material for lead-free MEMS applications.     

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS₂, TiSe₂, and TiTe₂ dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS₂ and TiTe₂. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS₂, TiSe₂, and TiTe₂ compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS₂ is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe₂ is caused by occupation of the 3d band in Ti.     

Pressure effect on magnetization for (CoTm)90Zr10 (Tm = Cr,Mo) amorphous alloys

Temperature dependences of the forced volume magnetostriction dω/dH and the saturation magnetization σ_s for (CoTm)₉₀Zr₁₀ (Tm = Cr, Mo) amorphous alloys have recently been measured by the 3-terminal capacitance method and a vibrating sample magnetometer and magnetic balance at temperatures from 77 K to the Curie temperature T_c or the crystallization temperature. The pressure coefficient of σ_s0 at 0 K, d ln σ_s0/dp, is estimated from (dω/dH)₀ extrapolated to 0 K using the thermodynamical relation. The values of d ln σ_s0/dp increase in negative value with increasing Tm concentration. The relation between d ln σ_s0/dp and the pressure coefficient of T_c, d ln T_c/dp, estimated indirectly from dω/dH is discussed.     

Energy band structure and X-ray emission spectra of ZrC and ZrN

Self-consistent augmented plane wave calculations are performed for ZrC and ZrN. The charge distributions resulting from valence bands in different regions of the unit cell are discussed and compared with related compounds, where the transition metal is varied between a 3d and 4d element of group IV and V. The limitations of the rigid band model are illustrated and general trends in the chemical bonding are discussed. In connection with X-ray emission spectra (XES) matrix element effects are shown for the three spectra Zr-L_III,-M_III, and-N_III. Further, comparison between theoretical and experimental XES is made with all data available for both ZrC and ZrN.     

Experimental determination of air-broadening parameters of pure rotational transitions of HNO3: intercomparison of measurements by using different techniques

We report on the air-broadening of the 44_d, 25 ← 44_d, 26, 43_d, 25 ← 43_d, 26, 25_d, 25 ← 24_d, 24, 27_d, 25 ← 27_d, 26, 26_1, 25 ← 26_0, 26, 15_13, 3 ← 14_13, 2, and 27_d, 27 ← 26_d, 26 transitions of HNO₃ at room temperature, which are useful for measurements of nitric acid in the Earth’s atmosphere by microwave limb sounders. In fact, the lines selection was essentially made on the basis of the spectral range requirements of MASTER, a limb sounding instrument managed by ESA. It is well established that the collisional-broadening parameters have a crucial influence on reduction of remote sensing data, but it is also well known that systematic errors make the evaluation of pressure-broadening parameters accuracy difficult. To this purpose, the investigation has been carried out in two different laboratories employing different techniques: the intercomparison allowed us to check the accuracy of the retrieved parameters as well as to estimate the extent of systematic errors affecting them.     

Hidden configurations and effective interactions: A comparison of three different ways to construct renormalized hamiltonians for truncated shell-model calculations

We discuss in general some criteria and methods for constructing effective Hamiltonians. Then three different methods are compared for constructing an effective Hamiltonian to be used in nuclear shell-model calculations for A = 17–20, allowing (A-16) active nucleons in the d_5/2, s_1/2 vector space. For all three methods, the aim is to obtain a d_5/2, s_1/2 model which will simulate the results of a given full d_5/2, s_1/2, d_3/2 model. The three methods for finding the effective Hamiltonian are.

1. (a) conventional low-order perturbation theory;

2. (b) a projection technique, in which we construct a Hamiltonian whose eigenvalues excactly match a selected subset of d_5/2, s_1/2, d_3/2 eigenvalues, and whose eigenvectors excatly match the projections of d_5/2, s_1/2, d_3/2 eigenvectors on the d_5/2, s_1/2 space; and

3. (c) least-square fit to selected d_5/2, s_1/2, d_3/2 energies.

For all three methods, we first restrict the effective Hamiltonian to a linear combination of 1-body and 2-body operators. Then for the perturbation and projection techniques, we also calculate the 3-body-operator terms in the effective Hamiltonian.When the effective Hamiltonians are limited to 1-body and 2-body terms, the leastsquare method yields the best overall fit to the low-lying spectrum of d_5/2, s_1/2, d_3/2     

高离化态类镍离子电子碰撞激发过程的相对论扭曲波理论研究

利用相对论扭曲波方法和新发展的研究电子碰撞激发过程的计算程序REIE06,系统计算了电子碰撞激发高离化态类镍Gd³⁶⁺和Rn⁵⁸⁺—U⁶⁴⁺(Z=86—92)离子从基态到4l(l=s,p,d,f)次壳层精细结构能级的碰撞强度和截面.研究了随等电子系列变化时,从基态到与X射线激光有关的3d⁹4p和3d⁹4d激发态能级的电子碰撞激发截面随Z的变化,讨论了强的组态相互作用对高离化态类镍离子截面的影响.通过对Gd³⁶⁺离子涉及X射线激光跃迁的相关能级电子碰撞激发速率系数的计算,分析了等离子体中电子温度对碰撞过程的影响.同时,目前部分计算结果与以往的理论结果进行了比较,得到了很好的一致性. 关键词： 电子碰撞激发 相对论扭曲波方法 高离化态类镍离子     

The study of the energy band structures of TiC,VC, Ti4C3 and V4C3 by the LMTO-ASA method

The energy band structures of TiC, VC, Ti₄C₃ and V₄C₃ have been studied by the linear muffin-tin-orbital method (LMTO). The influence of vacancies on the density of states (DOS) in the 2s C-band is a uniform reduction and a narrowing of this DOS. The splitting of the peak in the low-energy part of the 2p C, 3d Me-band (Me = Ti, V) is observed, while in the neighbourhood of the Fermi energy two peaks of DOS appear which consist of 3d Me- and vacancy states. Under the influence of vacancies the electronic charge in the carbon atomic sphere is shifted partly into the vacancy sphere. For Ti₄C₃, the increase of the Fermi energy and DOS at this energy is observed, while in the case of V₄C₃ these values decrease. In the presence of vacancies a contraction of crystal lattice is observed while the bulk moduli of TiC and VC diminish which is most pronounced for VC. The results are compared with previous data obtained by the LCAO coherent potential and APW calculations and with the experimental data concerning the DOS at the Fermi energy.