Theoretical Calculations of Rydberg Stark Effect of Hydrogen Atom

The Stark shifts and widths of the highly excited states near the classical ionization threshold of a hydrogen atom are calculated by the B spline technique plus complex scaling method. The Lanczos method has been used in our calculations and is proved to be powerful. Our results are in agreement with the experimental results and theoretical ones obtained by other methods. The method can also be used to calculate the same problem for atoms in parallel and cross electric and magnetic fields.     

Convergence of rayleigh-schrödinger perturbation theory in calculations of multiphoton processes

Abstract

We have calculated the high-order ac Stark Shift, multiphoton ionization rates, and nonlinear susceptibilities for high harmonic generation for the hydrogen atom in a radiation field. The calculations are done in the framework of Rayleigh-Schrödinger perturbation theory applied to a complex-rotated Hamiltonian. Our intention is to investigate the limitations of perturbation theory in calculations of multiphoton processes. Comparisons are made with results from nonperturbative calculations. For some frequencies the results of lowest-order perturbation theory are found to disagree with nonperturbative calculations even at moderate to low intensities (I ～ 10¹¹ W cm^?2) and in the absence of resonances. We find that the high-order perturbation expansion theory is not a reliable predictor of the behavior of hydrogen atoms in radiation fields with intensities greater than ～ 10¹² W cm^?2.     

硼掺杂富勒烯储氢-从物理吸附到化学吸附的转变

本文采用密度泛函理论(DFT)中的局域密度近似(LDA)方法对硼(B)掺杂富勒烯(C_(35)B)储氢问题在前人的基础上做了进一步研究,结果表明被C_(35)B吸附的氢分子很容易解离,经历从物理吸附到化学吸附的转变,并且发现解离产物C_(34)BHCH有分子内氢转移反应发生,这时B原子仍能与氢分子有很强的相互作用,最终导致B位置以及与B最邻近的三个C原子上都有氢原子吸附.并利用过渡态理论从热力学上分析了这种反应的发生趋势.     

Exceptional points in atomic spectra

We report the existence of exceptional points for the hydrogen atom in crossed magnetic and electric fields in numerical calculations. The resonances of the system are investigated and it is shown how exceptional points can be found by exploiting characteristic properties of the degeneracies, which are branch point singularities. A possibility for the observation of exceptional points in an experiment with atoms is proposed.     

Magnetic trapping of strongly-magnetized Rydberg atoms

Effective magnetic moments of drift Rydberg atoms in strong magnetic fields are obtained for different energy and angular-momentum states. Classical two-body trajectory calculations and quantum-mechanical one-body calculations are employed. For heavy atoms such as rubidium, the trapping dynamics can largely be explained by the net magnetic moment due to the cyclotron and the magnetron motion of the Rydberg electron. In light Rydberg atoms such as hydrogen, the intrinsic two-body nature of the dynamics becomes manifest in that the ionic motion significantly contributes to the effective magnetic moment. Also, light drift Rydberg atoms exhibit an anisotropic response to field-inhomogeneities parallel and transverse to the magnetic-field lines. The results are relevant to magnetic trapping of Rydberg atoms in strong-magnetic-field atom traps.     

Bound-state perturbation method via SVZ sum rules in quantum mechanics

The perturbation method for bound states within the framework of the Shifman-Vainshtein-Zakharov sum rule method is studied on simple systems (linear harmonic oscillator, hydrogen atom) in external electric fields. It is pointed out that for stronger fields reasonable results for the ground-state energy can only be achieved when sum rules are written for the correction to the Euclidean Green function caused by the external field. Moreover, if the system is bound by a singular (Coulomb) potential, one needs to sum higher perturbative corrections to the Green function and to find a realistic approximation of the continuum contribution to the sum rules. The results are of relevance e.g. for calculations of nucleon magnetic moments and toponium properties via SVZ sum rules in QCD.     

Cluster calculations of hydrogen in the grain boundaries of nickel

A series of self-consistent field, molecular orbital cluster calculations has been conducted to model the influence of hydrogen on certain structural units in the grain boundaries of nickel. The structural units considered were two Bernal polyhedra, namely the capped trigonal prism and the Archimedean antiprism. Other calculations were performed to simulate interstitial hydrogen and atomic hydrogen chemisorbed on the (111) surface. It was found that hydrogen causes local expansion as an interstitial impurity, in rough quantitative agreement with experiments on dilute solid solutions of hydrogen in nickel. In contrast, it was found that a single hydrogen atom causes a shrinkage of about 1.7% in the bond lengths of the capped trigonal prism and about 2.8% in those of the Archimedean antiprism. Similarly, a hydrogen atom chemisorbed above a nickel atom causes the nearest (111) surface bonds to shorten by about 1.7%. The shrinkage induced in the two Bernal polyhedra appears to be correlated to the low electron density at their centres, and the overall reduction of charge in the vicinity of certain nickel-nickel bonds upon the inclusion of the hydrogen atom.     

Ionization of atomic hydrogen by electron impact. Numerical calculations for the “free-fall” atomic model

The atomic model of the zero-angular momentum electron trajectory was used in numerical classical three-body calculations of hydrogen atom ionization by electron impact. The results are compared with the results for microcanonical model and with experimental data.     

Intermolecular Hydrogen Bonding of Poly(Imino Imino Ketone Ketone)

Molecular dynamics calculations were made of the distance from the hydrogen atom of the imino group to the distance of the oxygen atom of the carbonyl group of poly(imino imino ketone ketone) (PIIKK). The results showed that theoretically there was hydrogen bond formation between the hydroxyl group and the carbonyl group of PIIKK. The existence of the hydrogen bonding between the polymer chains of PIIKK was confirmed by infrared spectrum analysis. Due to the existence of the hydrogen bonding, the glass transition temperature increased to 273°C from 143°C for poly(ether ether ketone) (PEEK).     

On the chemisorption of hydrogen on lithium clusters

Ab-initio Hartree-Fock calculations for hydrogen atoms chemisorbed on lithium clusters have been performed using a basis which includes p-functions. No penetration of the hydrogen atom beyond the surface of the cluster was observed. The distance between the hydrogen atom and the nearest lithium atoms of the cluster becomes larger as the coordination number increases.     

Statistics and Correlation Properties of Diamagnetic High Rydberg Hydrogen Atom

The spectra of Rydberg hydrogen atom in magnetic fields have been calculated using linear variational method with B-splines basis functions [Acta Phys. Sin. 55 （2006） 3380]. Based on these calculations we have done some statistics analysis about the high Rydberg energy levels. The nearest-neighbor energy spacing distribution and the 3-statistics have been shown about diamagnetic Rydberg hydrogen atom with the magnetic field being 0.6 T and 6 T. The phenomena of multiply crossing, multiply anti-crossing, and the mixed of crossing and anti-crossing of energy levels have appeared in this paper. For both cases, in range of lower energy, the energy 1evel statistics properties close to Poisson distribution. With the increasing of the energy, the energy level statistics properties are away to Poisson distribution and tend to Wigner distribution step by step.     

The Zeldovich effect in a superstrong magnetic field

It follows from the analysis of the precision numerical calculations of the energy spectrum of a hydrogen atom in a static magnetic field that the Zeldovich effect (rearrangement of the atomic spectrum) in the spectrum of atomic levels is observed at superstrong magnetic fields B≥5×10₁₁ G. Magnetic fields of such strengths are reached in neutron stars and magnetic white dwarfs. We established a lower bound B_min for the fields required for this effect to occur.     

Estimate of the polarization fields of a relativistic atom in a solid

The magnetic and electric polarization fields of a relativistic hydrogen atom in a solid are analyzed. At atomic distances, these fields differ only slightly from the corresponding fields of an ionized atom.     

Theoretical study of hydrogen adsorption in Ti-decorated capped carbon nanotube

We present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses from adsorption energy profile, highest occupied molecular orbital–lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques.     

Resonances of a hydrogen atom in strong parallel electric and magnetic fields using B-spline basis sets

The B-spline basis set plus complex scaling method is applied to the numerical calculation of the exact resonance parameters $E_r}$ and $\Ga/2$ of a hydrogen atom in parallel electric and magnetic fields. The method can calculate the ground and higher excited resonances accurately and efficiently. The resonance parameters with accuracies of $10^{-9}-10^{-12}$ for hydrogen atom in parallel fields with different field strengths and symmetries are presented and compared with previous ones. Extension to the calculation of Rydberg atom in crossed electric and magnetic fields and of atomic double excited states in external electric fields is discussed.     

Resonances of a hydrogen atom in strong parallel electric and magnetic fields using B-spline basis sets

The B-spline basis set plus complex scaling method is applied to the numerical calculation of the exact resonance parameters Er and Г/2 of a hydrogen atom in parallel electric and magnetic fields. The method can calculate the ground and higher excited resonances accurately and efficiently. The resonance parameters with accuracies of 10^-9 - 10^-12 for hydrogen atom in parallel fields with different field strengths and symmetries are presented and compared with previous ones. Extension to the calculation of Rydberg atom in crossed electric and magnetic fields and of atomic double excited states in external electric fields is discussed.     

Elastic scattering of electrons by the metastable 2s state of atomic hydrogen

A two-potential approach is used to study the elastic scattering of electrons by the metastable hydrogen atom. The results or differential and total cross sections are presented at 200 and 400 eV energies and compared with the available calculations. Also a comparison between elastic scattering from 2s and 1s states of hydrogen is made.     

电子与氢原子碰撞激发（n=2,n=3态）微分散射截面理论计算

应用耦合通道光学势方法，计算了中等能量范围电子碰撞激发氢原子到ｎ＝２，ｎ＝３激发态以及弹性散射的微分散射截面，将计算结果同实验和其它理论方法进行了比较。     

Chemisorbed hydrogen: Electron scattering,resonance levels,and vibration frequency

Several physical properties of atomic hydrogen chemisorbed on tungsten are computed on the basis of our earlier density functional calculations. The differential scattering cross-section of 50–100 eV electrons by a chemisorbed hydrogen atom is computed and compared with that of an isolated hydrogen atom. The relevance of this cross-section to LEED experiments is discussed. An electronic resonance level associated with the hydrogen atom is found at 5.6 eV below the Fermi level, in very good agreement with recent photo-emission data. The vibrational excitation energy perpendicular to the metal plane is calculated to be 200 meV, compared to the observed 140 meV.     

Glauber exchange effect in the excitation of hydrogen by electron impact

The Glauber exchange effect is included into the calculations of differential cross sections in an analysis of 1–2 excitation of the hydrogen atom by electron impact within the conventional Glauber theory. An improvement of the theoretical results is obtained.