Calculations of Photo-Ionization Cross Sections for Lithium Atoms

Photo-ionization cross sections for the ground and the ≤5 excited states of lithium atoms are calculated in the photoelectron energy ranging from threshold to 0.5 Rydberg. The wavefunctions for both the bound and continuum states are obtained by solving the SchrSdinger equation numerically in a symplectic scheme. Our results are in excellent agreement with the recent experimental measurements and in harmony with other theoretical calculations.     

Semiclassical Calculations of Autoionization Rate for Lithium Atoms in Parallel Electric and Magnetic Fields

By using a semiclassical method, we present theoretical computations of the ionization rate of Rydberg lithium atoms in parallel electric and magnetic fields with different scaled energies above the classical saddle point. The yielded irregular pulse trains of the escape electrons are recorded as a function of emission time, which allows for relating themselves to the terms of the recurrence periods of the photoabsorption. This fact turns to illustrate the dynamic mechanism how the electron pulses are stochastically generated. Comparing our computations with previous investigation results, we can deduce that the complicated chaos under consideration here consists of two kinds of seff-similar fractal structures which correspond to the contributions of the applied magnetic feld and the core scattering events. Furthermore, the effect of the magnetic field plays a major role in the profile of the autoionization rate curves, while the contribution of the core scattering is critical for specifying the positions of the pulse peaks.     

Calculations of the Energies of the Excited States of Open-Shell Atoms in the Hartree-Fock Approximation

In the framework of the Roothaan-Hartree-Fock atomic theory, the solution of a many-electron problem is considered on the basis of the methods of minimizing a function of many variables. To implement this approach, expressions are obtained for the energy derivatives with respect to the elements of density matrices and the nonlinear parameters of atomic orbitals, that is, orbital exponents. Using the first- and second-order minimization methods, we performed optimization of the orbital exponents of Slater-type atomic orbitals for atoms and ions with several open shells. For them, energies that are close to the data of the numerical solution of the Hartree-Fock equations at a high accuracy of the virial ratio were determined. For a number of atoms the frequencies of the first dipole transitions were calculated, and the results were compared to the data obtained in calculation by the method of random phases and to experimental data. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 292–300, May–June, 2005.     

Polarizabilities and Hyperpolarizabilities for Lithium Atoms in Debye Plasmas

The effects of plasma environments on energies, oscillator strengths, polarizabilities and hyperpolarizabilities for lithium atom have been calculated by combining the l-dependent model potential of free lithium atom and linear variation method based on B-spline basis functions. The influence of plasma on lithium atom is represented by the Debye screened potential, which describes effectively the averaged effect of the plasma environment on atomic spectra. The results are in agreement with other reported ones.     

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。     

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。     

Entanglement of Two Atoms in Insulator and Superfluid States

We study two coupled cavities, each of which contains two two-level atoms. We identify the regions of Mott-insulator and superfluid states. Ground-state entanglement of two atoms in one cavity has been investigated. The result show that quantum entanglement of two atoms within one cavity can also characterize quantum phase transition.     

Bound States of Repulsing Adsorbed Atoms

JETP Letters - The interaction between two slow atoms adsorbed on the surface is considered. It is shown that, similar to Efimov states of three particles, this system has a bound state at any sign...     

氢化锂中氢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,对氢化锂中间隙氢离子的形成以及迁移行为进行了研究,结果表明间隙氢离子沿[1 1 1]方向迁移势垒最小,迁移到最近邻间隙和次近邻间隙时由其近邻氢离子主导的可能性更大,室温下间隙氢离子可自发迁移到最近邻间隙和第三近邻间隙.氢离子迁移到次近邻间隙和第四近邻间隙形成Frenkel缺陷的可能性最大,是形成Frenkel缺陷最可能的两个位置.     

Dynamics of Liquid Lithium Atoms. Pseudopotential and EAM-Type Potentials

It is generally accepted that the complicated character of the interparticle interaction in liquid metals is reproduced most correctly by many-particle potentials of the EAM-type (embedded atom model) interparticle interaction. It is shown that in the case of liquid lithium near the melting temperature (T_m = 453.65 K), the spherical pseudopotential provides a better agreement with experimental data on elastic and inelastic X-ray scattering as compared to the known EAM potentials. The calculations of the dynamic structural factor and spectral densities of the longitudinal and transverse atomic currents lead to the conclusion that although the pseudopotential and EAM potentials generate a certain qualitative correspondence in the features of collective dynamics, the interparticle interaction of the spherical type reproduces correctly the general form of the dynamic structure factor in a certain wavenumber range, as well as the dispersion relation for collective excitations.     

Collisions with Participation of Polarized Cesium and Lithium Alkali Atoms

Optics and Spectroscopy - The spin-exchange cross sections and the magnetic resonance frequency shift in collision of lithium and cesium atoms in the ground state are calculated. The calculations...     

高电离态原子光谱测量

简要介绍了兰州重离子加速器上的高电离态原子光谱实验测量和取得的部分实验结果.The excitation spectra and level lifetimes of highly charged atoms for heavier elements of Ne, S and Ar have been measured by using the beam foil method on the heavy ion accelerator in Lanzhou. Emission spectra in the wavelength region of 25-400  was studied. On the whole, the agreement between our experimental results and other experiments is fairly good.     

Enhanced Raman Scattering by Quasi-phase-matched Processes in ax^（2） Photonic Crystal

An intense comb-shaped Raman spectra were obtained from a two-dimensional nonlinear x（2） photonic crystal - a hexagonally poled LiTaO3 crystal with lattice parameter 9 micros. The lowest Raman shift was down to 2 cm^-1 and the order of anti-stokes and stokes signals both achieved 11. The novel Raman spectra were mediated first by intense phonon-polariton fields, which were driven through the quasi-phase-matched coupling between the incident dual-beam both from an optical parametric oscillation laser, and further amplified greatly also by such quasi-phasematched nonlinear optical process. The dependence of the Raman spectra character on the wavelength and intensity of incident beams were studied in detail, which accordingly revealed information of the inelastic scattering and the elementary excitation in the nonlinear medium. These results on the other hand suggest technological importance for developing a novel Raman laser with the multi-wavelength output and a tunable frequency interval and for possible applications in quantum optics.     

Scattering of Light Exotic Atoms in Excited States

The scattering of light exotic atoms in excited states (n = 2–5) from hydrogen has been calculated in a close-coupling model. For the first time, the absorption cross sections for hadronic atoms due to Stark collisions have been calculated by taking the shifts and widths of the nS states into account in a self-consistent quantum mechanical framework. A classical-trajectory Monte Carlo method has been used to calculate the scattering of exotic atoms from molecular hydrogen for n≥8. The Coulomb transitions with Δn>1 are found to be the dominant deexcitation mechanism at the initial stage of the cascade.     

Entanglement Entropies in the Ground States of Helium-Like Atoms

We examine the entanglement in the ground states of helium and helium-like ions using an original Hylleraas expansion. The von Neumann and linear entropies of the reduced density matrix are accurately computed by performing the Schmidt decomposition of the S singlet spatial wavefunctions. The results presented are more accurate than currently available in published literature.     

Covalency Measurements via NMR in Lithium Metal Phosphates

³¹P nuclear magnetic resonance (NMR) shifts on the order of thousands of parts per million are observed for olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples, a promising class of Li ion rechargeable battery electrode materials. Variable-temperature ³¹P NMR measurements of shift are used to determine that the supertransferred hyperfine interaction is the dominant mechanism giving rise to these unusually large observed ³¹P shifts. Various models for predicting ³¹P and ⁷Li shifts in LiMPO₄ (M = Mn, Fe, Co, Ni) were investigated. Alloys of LiFe_1−x Mn _x PO₄, where x varies from 0 to 1, were also investigated by ⁷Li NMR. Covalency constants, calculated from variable-temperature NMR shifts and magnetic susceptibility data, are determined for the P–O–M bonds in LiMPO₄ (M = Mn, Fe, Co, Ni) and compared to the covalency constants of the Li–O–M bond. The sign and relative magnitude of the covalency constants are discussed in terms of positive and negative spin densities at the nuclei of interest. The covalency constants for the Li–O–M and P–O–M bonds were measured for Li_1.8Na_0.2FeMn₂(PO₄)₃ and compared to the covalency constants measured in the olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples. The Li_1.8Na_0.2FeMn₂(PO₄)₃ structure has a volume per transition metal atom and Li–O–M bond distances that are similar to those of the olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples. Authors' address: Jeffrey A. Reimer, Department of Chemical Engineering, University of California Berkeley, Berkeley, CA 94720, USA