BF自由基X1∑+和a3∏态光谱常数和分子常数研究

采用内收缩多参考组态相互作用方法和相关一致基aug-cc-pV6Z, 对BF自由基X¹∑⁺和a³∏ 态的势能曲线进行了研究. 计算是在0.095---1.33 nm的核间距内进行的. 为获得更准确的结果, 计算中还考虑了Davidson修正、相对论修正及核价相关修正对势能曲线的影响. 相对论修正采用的方法是二阶DouglasKroll哈密顿近似, 修正计算是在cc-pV5Z基组水平上进行的. 核价相关修正使用的是cc-pCV5Z基组. 利用得到的势能曲线, 拟合出了各种修正下BF自由基X¹∑⁺和a³∏ 态的光谱常数D_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e和α_e、并与实验结果进行了比较. 结果表明: 考虑Davidson修正、相对论修正和核价相关修正后得到的光谱常数最接近实验结果. 利用修正后的势能曲线, 通过求解径向振转Schrödinger方程, 找到了转动量子数J = 0时这两个电子态的全部振动态, 并计算了每一电子态前20个振动态的振动能级、惯性转动常数和离心畸变常数, 其值与已有的实验结果较为一致. 本文得到的光谱常数和分子常数达到了很高的精度, 能为进一步的光谱实验提供可靠的参考.     

On the electronic properties of the sulfur nitride polymer (SN)x

Results of an ab initio LCAO Hartree-Fock crystal orbital calculation are reported for (SN)_x using a double-zeta type atomic basis set. In contrast with previous minimal basis calculations the width of the metallic half-filled band is only ～ 4 eV in this study. The calculated effective mass (1.7m_e), electron state density [0.14/(ev spin molecule)] and transferred charge (～0.4e from sulfur to nitrogen) are also in good agreement with experiment.     

Probabilities for electronic transitions of molecular systems of high-temperature air components—I. The schumann-runge system of the O2-molecule and the first positive system of the N2-molecule

The results for absolute and relative probabilities for electronic transitions of the Schumann-Runge system of the O₂-molecule and the first positive system (1+) of the N₂-molecule published elsewhere have been critically analyzed. For the S-R system, statistical processing of the experimental results for absolute and relative probabilities on a joint basis made it possible to establish a new dependence of the electronic transition strength on the internuclear separations S_e(r_v′v″), which reliably describes the behaviour of S_e over the whole spectral range. For the (1+) system of the N₂-molecule, it has been shown that none of the published dependences S_e(r_v′v″) provide acceptable fits to the measured results on absolute intensities and life-times. In practical calculations, one should use the dependence given in Ref. 41, which is derived from relative intensities and corroborated by absolute intensity measurements.     

A new upper limit for the branching ratio of the decay K0S → e+e−

A new value of the upper limit for the branching ratio of the decay of K⁰_S into e⁺e⁻ has been experimentally obtained using a lead glass detector. The value is BR (K⁰_S → e⁺e⁻) < 1.1 × 10⁻⁴ (90% CL).     

One and two-photon detachment cross-sections of Ps-

We present detailed calculations for one- and two-photon above-threshold detachment (ATD) cross-sections of the negative positronium ion Ps ^- ( e ⁺ e ^- e ^- ), below the threshold of Ps(n = 2), using a configuration interaction (CI) method on a B splines basis. Both the one- and two-photon detachment cross-sections have a form similar to the corresponding spectra of the H^- ion, scaled accordingly. The peak value of the one-photon cross-section agrees very well with the calculations by Bathia and Drachman [1], while it differs from those by Igarashi et al. [2], which give a value of 15% lower. Two-photon detachment cross-sections are also reported. Received 24 January 2002 / Received in final form 9 April 2002 Published online 19 July 2002     

MRCI study on spectroscopic and molecular properties of several low-lying electronic states of the CN radical

The potential energy curves (PECs) of eight low-lying electronic states (X²Σ⁺, A²Π, B²Σ⁺, a⁴Σ⁺, D²Π, E²Σ⁺, 1²Σ⁻ and F²Δ) of the CN radical have been studied using the ab initio quantum chemical method. The calculations have been performed using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core-valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas-Kroll Hamiltonian approximation. The core-valence correlation correction calculations are performed with the cc-pCVQZ basis set. The relativistic correction is carried out at the level of cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (T_e, R_e, ω_e, ω_ex_e, ω_eу_e, B_e, α_e and γ_e) are determined and compared with those reported in the literature. Finally, with the PECs obtained by the MRCI+Q/CV+DK+Q5 calculations, the complete vibrational states are computed for the eight electronic states by solving the ro-vibrational Schrödinger equation for the non-rotating radical, and the vibrational levels and inertial rotation and centrifugal distortion constants of the first 11 vibrational states are reported, which agree favorably with the available experimental data. The spectroscopic parameters of 1²Σ⁻ and F²Δ electronic states obtained by the MRCI+Q/CV+DK+Q5 calculations should be good predictions for future laboratory experiments.     

Effects of Kr and Xe ion irradiation on the structure of Y2O3 nanoprecipitates in YBCO thin film conductors

ABSTRACT

The response of Y₂O₃ nanoprecipitates in a 1-µm YBa₂Cu₃O_7-x layer from a superconducting wire Ag/YBCO/buffer metal oxides/Hastelloy to 107?MeV Kr and 167?MeV Xe ion irradiation was investigated using a combination of transmission electron microscopy, diffraction and X-ray energy-dispersive spectrometry. The direct observation of the radiation-induced tracks in Y₂O₃ nanocrystals is reported for the first time to the authors’ best knowledge. Structureless damaged regions of 5–9?nm (average 8?nm) in diameter were observed in Y₂O₃ nanocrystals when the electronic stopping power S_e was about or higher than 4.7 keV/nm. This value of S_e is the upper estimate of the minimum electronic stopping power to create damage in yttria nanocrystals. The electron diffraction patterns, high-resolution transmission electron microscopy, high-resolution scanning transmission electron microscopy, Fourier transform patterns from areas extending a few nanometres around the tracks show that yttria and YBCO keep their respective cubic and orthorhombic pristine structures.     

Ab initio calculations on the spectroscopic constants, vibrational levels and classical turning points for the 21∏u state of dimer 7Li2

The accurate dissociation energy and harmonic frequency for the highly excited 2^1Пu state of dimer ^7Li2 have been calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space. The calculated results are in excellent agreement with experimental measurements. The potential energy curves at numerous basis sets for this state are obtained over a wide internuclear separation range from about 2.4a0 to 37.0a0. And the conclusion is gained that the basis set 6-311＋＋G（d,p） is a most suitable one. The calculated spectroscopic constants De, Re, ωe, ωeχe, ae and Be at 6-311＋＋G（d,p） are 0.9670 eV, 0.3125 nm, 238.6 cm^-1, 1.3705 cm^-1, 0.0039 cm^-1 and 0.4921 cm^-1, respectively. The vibrational levels are calculated by solving the radial SchrSdinger equation of nuclear motion. A total of 53 vibrational levels are found and reported for the first time. The classical turning points have been computed. Comparing with the measurements, in which only the first nine vibrational levels have been obtained so far, the present calculations are very encouraging. A careful comparison of the present results of the parameters De and We with those obtained from previous theories clearly shows that the present calculations are much closer to the measurements than previous theoretical results, thus representing an improvement on the accuracy of the ab initio calculations of the potentials for this state.     

Magnetic field dependence of the thermoelectric power of n - type gallium arsenide in the extreme quantum limit

The effect of the quantization of the electron energy levels in a strong transverse magnetic field H on the low-temperature thermoelectric power (TEP) S of a high-purity isotropic semiconductor ($\text{n}$ - type gallium arsenide GaAs) is investigated theoretically. The “electron-diffusion” (S_e) and “phonon-drag” (S_p) components of S( = S_e + S_p) are calculated in the extreme quantum limit, when all the electrons in the conduction band are concentrated in the lowest Landau level. The transition to nondegeneracy, which takes place when the bottom of the lowest Landau level is driven through the Fermi level, has a large effect on the variations of S_e and S_p with magnetic field. The results are illustrated with numerical calculations for $\text{n}$ - type GaAs at 4.2 K with 1.2 × 10¹⁶ cm^-3 electrons.     

Oscillations of the magnetoresistance in an inclined magnetic field for MIS structures on (100) silicon with a high electron density

At electron densities N _S>6×10⁻² cm⁻²² a second series of oscillations, which are tentatively attributed to population of the second energy subband, is observed in addition to the main series of Shubnikov-de Haas oscillations. A change in phase of the oscillations of the second series is observed at some angle of inclination α_e of the field. The measured value of α_e is used to calculate the ratio of the cyclotron mass to the effective g factor. The maximum possible cyclotron mass is also determined as m _H< 0.32m _e. On this basis it is concluded that the second series of oscillations is due to electrons which have an in-plane effective mass m*≈0.2m _e and which belong to the same valleys of the Fermi surface as in the case of the main oscillations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 136–140 (25 January 1998)     

MRCI+Q理论研究SiSe分子X1Σ+和A1Π电子态的光谱常数和分子常数

采用Davidson修正的内收缩多参考组态相互作用方法(MRCI+Q)及相关一致基aug-cc-pV5Z和aug-cc-pVQZ分别计算了SiSe分子X¹Σ⁺和A¹Π电子态的势能曲线. 为提高势能曲线的计算精度, 利用两点总能量外推公式, 将两个电子态的势能曲线外推至完全基组极限, 并对其进行了标量相对论修正, 相对论效应是在cc-pV5Z基组水平下使用三级Douglas-Kroll-Hess哈密顿算符计算的. 利用MRCI+Q/Q5+DK理论水平的势能曲线获得了这两个态的光谱常数(T_e, D_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e和α_e)和J=0时前30个振动态的B_υ和D_υ等分子常数. 其值与已有的实验结果非常一致. 本文得到的光谱常数和分子常数达到了很高精度, 能为进一步的光谱实验和理论研究提供可靠参考. 关键词： 势能曲线 基组外推和标量相对论修正 光谱常数 分子常数     

Numerical solution of radiative and conductive heat transfer in concentric spherical and cylindrical media

A new technique is presented to improve the performance of the discrete ordinates method when solving the coupled conduction-radiation problems in spherical and cylindrical media. In this approach the angular derivative term of the discretized one-dimensional radiative transfer equation is derived from an expansion of the radiative intensity on the basis of Chebyshev polynomials. The set of resulting differential equations, obtained by the application of the S_N method, is numerically solved using the boundary value problem with the finite difference algorithm. Results are presented for the different independent parameters. Numerical results obtained using the Chebyshev transform method compare well with the benchmark approximate solutions. Moreover, the new technique can easily be applied to higher-order S_N calculations.     

Sr-doping enhanced electrical transport and thermionic emission of single crystal 12CaO·7Al2O3 electride

Sr-doped single crystals (C_1-xS_x)12A7:e⁻ (x = 0, 0.01, 0.02, 0.03) were successfully fabricated by floating zone method. It is found that Sr-doping decreases the reduction time from 30 h to 20 h. The maximum emission current of (C_1-xS_x)12A7:e⁻ is greatly improved by 50% than that of the un-doped. The DFT calculations show Sr-doping in C12A7 contributed to the free O²⁻ in the cages spread out, leading to a short reduction time; increase the “window” between two adjacent cages that is conducive to the electrons in cages to escape. And the work function of the (C_1-xS_x)12A7:e⁻ is lower than that of C12A7:e⁻.     

The effect of gamma irradiation on carbon fibre properties

Abstract

The method given by Pekeris for He-atom and generalized recently by Frost for three-particle system is applied to calculate the binding energies of excitons bound to ionized donors and acceptors. The calculations are carried out for different values of γ = m_e?/m_h? where m_e? and m_k ? are the effective masses of the electron and the hole respectively. For ionized donors the system is stable for γ < 0. 32. In semiconductors where excitons are bound to ionized acceptors the value of γ > 0. 227 is necessary to provide a stable system.     

Probing the basis set limit for thermochemical contributions of inner-shell correlation: balance of core-core and core-valence contributions*

ABSTRACT

The inner-shell correlation contributions to the total atomisation energies of the W4-17 computational thermochemistry benchmark have been determined at the CCSD(T) level near the basis set limit using several families of core correlation basis sets, such as aug-cc-pCVnZ (n?=?3–6), aug-cc-pwCVnZ (n?=?3–5) and nZaPa-CV (n?=?3–5). The three families of basis sets agree very well with each other (0.01?kcal/mol RMS) when extrapolating from the two largest available n: however, there are considerable differences in convergence behaviour for the smaller basis sets. nZaPa-CV is superior for the core-core term and awCVnZ for the core-valence term. While the aug-cc-pwCV(T+d)Z basis set of Yockel and Wilson is superior to aug-cc-pwCVTZ, further extension of this family proved unproductive. The best compromise between accuracy and computational cost, in the context of high-accuracy computational thermochemistry methods, is CCSD(T)/awCV{T,Q}Z, where the {T,Q} notation stands for extrapolation from the awCVTZ and awCVQZ basis set pair. For lower-cost calculations, we recommend a previously proposed combination of CCSD-F12b/cc-pCVTZ-F12 and CCSD(T)/pwCVTZ(no f). While in first-row molecules core-valence correlation on average accounts for over 90% of the inner-shell contribution, in second-row molecules core-core contributions may become important, particularly in systems like P₄ and S₄ with multiple adjacent second-row atoms.     

DFT studies of the molecular nanomagnet Fe 8 and the V 15 spin system

Based on first-principles all-electron density-functional calculations we report the electronic structure and magnetic ordering of the molecular magnet Fe₈ and the V₁₅ spin system. The ferrimagnetic ordering with total spin S = 10 of the eight iron atoms in the Fe₈ cluster agrees well with experimental results from polarized neutron data. In comparison the low spin system V₁₅ shows a spin S = 1/2 ground state which is also found from our calculations. Received 30 October 2000     

PLE spectra analysis of the sub-structure in the absorption spectra of CdSeS quantum dots

The semiconductor CdSeS quantum dots (QDs) embedded in glass are analysed by means of absorption spectra, photoluminescence (PL) spectra and photoluminescence excitation (PLE) spectra. The peaks of absorption spectra shift to lower energies with the size of QD increasing, which obviously shows a quantum-size effect. Using the PLE spectra, the physical origin of the lowest absorption peak is analysed. In PLE spectra, the lowest absorption peak can be deconvoluted into two peaks that stem from the transitions of 1S_3/2--1S_e and 2S_3/2--1S_e respectively. The measured energy difference between the two peaks is found to decrease with the size of QD increasing, which agrees well with the theoretical calculation for the two transitions. The luminescence peak of defect states is also analysed by PLE spectra. Two transitions are present in the PLE, which indicates that the transitions of 1S_3/2--1S_e and 2S_3/2--1S_e are responsible for the defect states luminescence.     

Electromagnetic momentum in frontiers of modern physics

We review the role of the momentum of the electromagnetic (EM) fields P _e in several areas of modern physics. P _e represents the EM interaction in equations for matter and light waves propagation. As an application of wave propagation properties, a first order optical experiment which tests the speed of light in moving rarefied gases is presented. Within a classical context, the momentum P _e appears also in proposed tests of EM interactions involving open currents and angular momentum conservation laws. Moreover, P _e is the link to the unitary vision of the quantum effects of the Aharonov-Bohm (AB) type and, for several of these effects, the strength of P _e is evaluated. These effects provide a quantum approach to evaluate the limit of the photon mass m _ph. A new effect of the AB type, together with the scalar AB effect, provides the basis for table-top experiments which yield the limit m _ph = 9.4 × 10⁻⁵²g, a value that improves the results achieved with recent classical and quantum approaches.      

A new basis set for molecular wavefunctions

A new basis set is proposed for molecular self-consistent field and configuration interaction calculations. Expansion functions are proposed in the form sin (r _A · p) exp (-ar_A ²) and cos (r _A · p) exp (-ar _A ²) and it is suggested that they are used as an alternative to the gaussian basis set x_A ⁱy_A ^jz_A ^k exp (-ar _A ²).

It is shown how the new basis can have the same effects, for suitable vectors p, as the gaussian basis. It is further shown that all the one and two-electron integrals in the new basis are evaluable in terms of exponentials, square roots and the complex error function erf (z). First calculations, using the new basis, are presented in LiH, HF and H₂O.     

The distance dependence and spatial distribution of the molecular quadrupole moments of P2, S2 and Cl2

The quadrupole moments (Θ) of the molecules P₂, S₂ and Cl₂ have been computed at the SCF, CASSCF and CASSCF + 1 + 2 levels of theory, using augmented correlation consistent basis sets. The convergence of Θ as a function of basis set and level of theory is discussed. The variation of Θ from the separated atoms to the equilibrium region is reported. Θ is written as the sum of a sigma and pi contribution, and inaccuracies in the SCF values for P₂ and S₂ are due to the poor representation of the pi system in the SCF theory. A reference state dependent quadrupole moment density, - ½(3cos² θ- 1)r ²δη(r; R), is defined whose integral is the mole2 cular quadrupole moment, and the spatial distributions of the density and its relationship to the density difference δη(r; R) are examined.