The dynamical properties of Rydberg hydrogen atom near a metal surface

The dynamical properties of Rydberg hydrogen atom near a metal surface are presented by using the methods of phase space analysis and closed orbit theory. Transforming the coordinates of the Hamiltonian, we find that the phase space of the system is divided into vibrational and rotational region. Both the Poincaré surface of section and the closed orbit theory verify the same conclusion clearly. In this paper we choose the atomic principal quantum number asn=20. The dynamical character of the exited hydrogen atom depends sensitively on the atom-surface distanced. Whend is sufficiently large, the atom-surface potential can be expressed by the traditional van der Waals force and the system is integrable. Whend becomes smaller, there exists a critical valued _c. Ford>d _c, the system is near-integrable and the motion is regular. While chaotic motion appears ford<d _c, and the system tends to be non-integrable. The trajectories become unstable and the electron might be captured onto the metal surface.     

The dynamical properties of a Rydberg hydrogen atom between two parallel metal surfaces

This paper presents the dynamical properties of a Rydberg hydrogen atom between two metal surfaces using phase space analysis methods. The dynamical behaviour of the excited hydrogen atom depends sensitively on the atom--surface distance d. There exists a critical atom--surface distance d_c = 1586 a.u. When the atom--surface distance d is larger than the critical distance d_c, the image charge potential is less important than the Coulomb potential, the system is near-integrable and the electron motion is regular. As the distance d decreases, the system will tend to be non-integrable and unstable, and the electron might be captured by the metal surfaces.     

外电场中金属表面附近里德堡氢原子的动力学行为

利用相空间分析方法研究了外电场中金属表面附近里德堡氢原子的动力学性质. 结果表明, 体系的动力学性质敏感地依赖于原子与金属表面间的距离和电场强度.通过固定原子与金属表面间的距离, 分析了外加电场作用下里德堡电子的Poincaré 截面和运动轨迹的演化过程. 研究表明: 电场的出现加速了金属表面对电子的吸附, 随着电场强度的增加,体系的动力学性质由原子与金 属表面间的距离控制逐渐变为由电场起主导作用,体系逐渐由不可积变为可积, 电子的运动轨道最终全部变为振动型轨道. 关键词： Poincaré截面 相空间分析方法 里德堡氢原子     

The closed-orbit and the photoabsorption spectra of the Rydberg hydrogen atom between two parallel metallic surfaces

Using the closed orbit theory, we study the classical motion and calculate the photoabsorption spectra of Rydberg hydrogen atom between two parallel metallic surfaces. The results show that the metallic surfaces have a significant effect on the photoabsorption process. When the distances between the hydrogen atom and the two metallic surfaces are close to a critical value d_c, the number of the closed orbits is the greatest. When the distance larger or smaller than d_c, the number of the closed orbits decreases and the absorption spectra are shown to exhibit a damping oscillation. This work is an interesting new application of closed-orbit theory and is of potential experimental interest.     

Absorption and Recurrence Spectra of Nonhydrogenic Rydberg Atom Near a Metal Surface

Multielectron to theoretical treatments atoms near a metal surface are essentially more complicated than hydrogen atom with regard By using the semicalssical dosed orbit theory generalized to the multielecton atoms, we study the dynamical properties of the Rydberg lithium atom near a metal surface. The photoabsorption spectra and recurrence spectra of this system have also been calculated. Considering the effect of the ionic core potential of the Rydberg lithium atom, the number of the closed orbits increases, which leads to more peaks in the recurrence spectra than the case of hydrogen atom near a metal surface. This result shows that the core-scattered effects play an important role in nonhydrogenic atoms. This study is a new application of the closed-orbit theory and is of potential experimental interest.     

双平行金属板间的里德堡氢原子的动力学性质

用相空间分析方法研究了双金属板间里德堡氢原子的动力学性质.结果表明：标度变换后,其动力学行为敏感地依赖于标度能量 .当标度能量 较小时,体系是近可积的,规则的,随着标度能量的增大,体系是不可积的,运动是混沌的,电子可能被金属表面俘获.     

Ab-initio molecular dynamical study of a single transition metal atom on fullerene C<Subscript>60</Subscript>: the case of Ta

We report the first-principles Car-Parrinello molecular dynamics study of the behaviour of a single transition metal Ta atom on fullerene C₆₀, at different temperatures, and for both neutral and charged clusters. We seek to characterise the motion of the lone Ta metal atom on the C₆₀ surface, contrasting its behaviour both with that of three Ta atoms, as well as with a single alkali metal atom on the cage surface. Our earlier simulations on C₆₀Ta₃ had revealed that the Ta atoms on the surface of the fullerene are affected by a rather high mobility, and that the motion of these atoms is highly correlated due to Ta-atom-Ta-atom attraction. Earlier, experimental studies of a single metal atom (K, Rb) on the surface of a C₆₀ molecule had led to the inference that at room temperature the metal atom skates freely over the surface, the first direct evidence for which was presented by us in earlier first principles molecular dynamical simulations.     

Recurrence Spectra of the Rydberg Hydrogen Atom near Two Parallel Metal Surfaces

Using closed orbit theory, we study the influence of the two parallel metal surfaces on the recurrence spectra of a hydrogen atom placed in the region between the two surfaces. The results show that the metal surfaces have significant effect on the photoabsorption process. Each resonance peak in the recurrence spectra is associated with one electronic closed orbit. In our work, we put the first metal surface at the critical value dc and vary the second metal surface. The results show that when the distances between the hydrogen atom and the two metal surfaces are close to the critical valuedc, the number of the closed orbits is the greatest and there are more peaks in the recurrence spectra. When the distance between the atom and the second metal surface is larger or smaller than dc, the number of the closed orbits decreases and there are fewer peaks in the recurrence spectra. The agreement between the semiclassical calculation spectra and the quantum calculation spectra suggests that our analysis is correct.     

氢负离子在微腔中的光剥离研究

利用闭合轨道理论,研究了氢负离子在金属面和弹性界面组成的微腔中的光剥离截面.结果表明,微腔的上下表面对氢负离子的光剥离截面产生很大影响.若固定金属面与氢负离子之间的距离不变,当弹性界面与氢负离子之间的距离很大时,弹性界面对氢负离子光剥离截面的影响很小,光剥离截面的振荡幅度和振荡频率与只有金属面时的情况类似.随着弹性界面和氢负离子之间距离的不断减小,光剥离截面的振荡幅度增大,振荡频率减小.若保持氢负离子和弹性界面之间的距离不变,随着金属面和氢负离子之间距离d₀的不断增大, 关键词： 光剥离截面 闭合轨道理论 微腔     

Analysis of the time-domain spectrum of hydrogen in electric field near helium surface

The Ryderberg electronic wave packet dynamics of hydrogen atom near helium surface in an electric field is investigated using the semiclassical method.The autocorrelation function is calculated when the photoionized electron is excited by a short laser pulse for different atom-surface separations.The results show that new recurrences appear because of the helium surface,and the number of recurrent peaks increases with the decrease in atom-surface distance.The new feature is ascribed to the bifurcation of new closed orbits in the classical dynamics of the photoionized electron.Therefore,surface properties have a significant effect on the spectrum of nearby atoms or ions.     

Examples of quantisable dynamical systems: The hydrogen atom and automorphism groups

The regularised energy surface of then-dimensional hydrogen atom is shown to be naturally the total space of a quantisable dynamical system. The automorphism groups of dynamical systems are studied; and the connected Riemannian dynamical systems with automorphism groups of maximal dimension are classified. Finally, the compact, connected and simply connected quantisable dynamical system with automorphism group of maximal dimension is shown to be the set of independent harmonic oscillators with equal periods.This research was supported in part by NSF GP-20856A, No. 1.     

Correspondence between classical dynamics and recurrence spectra of Rydberg hydrogen atom near a metal surface

The chaotic behaviours of the Rydberg hydrogen atom near a metal surface are presented. A numerical comparison of Poincare surfaces of section with recurrence spectra for a few selected scaled energies indicates the correspondence between classical motion and quantum properties of an excited electron. Both results demonstrate that the scaled energy dominates sensitively the dynamical properties of system. There exists a critical scaled energy εc, for ε 〈 εc, the system is near-integrable, and as the decrease of ε the spectrum is gradually rendered regular and finally turns into a pure Coulomb field situation. On the contrary, if ε 〉 εc, with the increase of ε, the system tends to be non-integrable, the ergodic motion in phase space presages that chaotic motion appears, and more and more electrons are adsorbed on the metal surface, thus the spectrum becomes gradually simple.     

Quantum dynamics of hydrogen atom in complex space

We show in this paper that the electron’s quantum dynamics in hydrogen atom can be modeled exactly by quantum Hamilton-Jacobi formalism. It is found that the quantizations of energy, angular momentum, and the action variable ∫p dq are all originated from the electron’s complex motion, and that the shell structure observed in hydrogen atom is indeed originated from the structure of the complex quantum potential, from which the quantum forces acting upon the electron can be uniquely determined, the stability of atomic configuration can be justified, and the electron’s complex trajectories can be derived accordingly. Based on the derived electron’s trajectory, we can explain why the electron appears at some positions with large probability, while at some other positions with small probability. The positions with maximum probability predicted by standard quantum mechanics are found to be just the stable equilibrium points of the electron’s non-linear complex dynamics. The electron’s trajectories in hydrogen atom are discovered to be very diverse and strongly state-dependent; some of them are open and non-periodic, while some are closed and periodic. Over such a great diversity of orbits, commensurability condition ensuring the existence of closed orbit will be derived and the de Broglie’s standing wave pattern will be identified. Along the investigation of the electron’s orbits in hydrogen atom, we will also clarify why old quantum mechanics using the concept of classical orbit can correctly predict the energy quantization of hydrogen atom and meanwhile why it is not applicable to general quantum system. Finally, the internal mechanism of how the precessing, non-conical eigen-trajectories can evolve continuously to the classical, non-precessing, conical orbits as n → ∞ is explained in detail.     

阶梯化对快离子导体LixTiS2的结构与能量性质的影响

根据密度波理论建立了stage-2有序Li_xTiS₂(x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序Li_xTiS₂(x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量c(d关键词： xTiS₂')" href="#">Li_xTiS₂ 阶梯结构 有序—无序相变 第一性原理计算     

The deformation producing tendency of (d 3/2−f 7/2) empirical effective interaction

The effective matrix elements in (d _3/2−f _7/2)² configuration have been recently defined by Erskineet al. and Sherret al. assuming shell clcsures for S³² and Ca⁴⁰. We have attempted to verify whether this empirically deduced (d _3/2−f _7/2)² interaction permits thed _3/2 shell to remain closed when nucleons are added to Ca⁴⁰. It is found that the Erskine interaction gives rise to ground states of thef _7/2 shell nuclei in which thed _3/2 orbit is completely filled. However that interaction over-binds Ca⁴⁰. If the centroid of the (d _3/2)² interaction is modified to fit the Ca⁴⁰ binding energy, the ground states of Cr⁴⁸ and Fe⁵² become deformed and thed _3/2 orbit is not completely filled.     

Photoionization microscopy of hydrogen atom near a metal surface

We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom-surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields.     

Structural and magnetic properties of Ti12M clusters (M=Sc to Zn)

The geometries, electronic, and magnetic properties of the 3d atom doped icosahedron (ICO) Ti₁₂M (M=Sc to Zn), where a dopant atom replaces either the centra l(Ti₁₂M^c) or surface (Ti₁₂M^s) Ti atom in ICO Ti₁₃ cluster, have been systematically investigated by using the density functional theory. The structures of all the optimized Ti₁₂M^c and Ti₁₂M^s clusters are distorted ICO. Sc, Ni, Cu, and Zn atoms prefer to displace surface Ti atom, V, Cr, Mn, and Fe atoms prefer to displace central Ti atom. The position of impurity atom depends on the strength of the interaction between the central atom and the surface atoms. As compared to the pure Ti₁₃ cluster, Ti₁₂M^c and Ti₁₂M^s (M=V, Fe, Co, and Ni) clusters are more stable, Ti₁₂M^c and Ti₁₂M^s (M=Sc, Cr, Mn, Cu, and Zn) are less stable. Both Ti₁₂Ni^s and Ti₁₂Ni^c are magic clusters, which originate from their electronic as well as geometric closed shells. Because the exchange interaction prevails over the crystal field in Ti₁₂M clusters, the valence electrons fill molecular orbitals in terms of Hund’s rule of maximum spin.     

Magnetic properties and hydrostatic pressure effect on the curie temperature of (Co,Mn)2B amorphous alloys

The temperature dependence of magnetization and magnetic susceptibility and hydrostatic pressure effect on the Surie temperature (dT_c/dP) are measured for (Co_1-xMn_x)₂B (0?x?0.4) amorphous alloys and the results are compared with those of crystalline compounds with the same composition. The Curie temperature decreases linearly with an increasing Mn content but magnetization shows a maximum around x=0.15. The reciprocal magnetic susceptibility of all the prepared alloys obeys the Curie-Weiss law above T_c. The magnitude of the negative value of dT_c/dP decreases linearly with increasing x from about 1.1 K/kbar (x=0) to zero (x=0.4), the composition dependence of which is opposite to that of the crystalline compound. The composition dependence of the average magnetic moment per transition metal atom and the Curie temperature and dT_c/dP are analysed on the basis of the local environment and the pair order interaction mode, respectively.     

Electrical breakdown as an insulator-to-metal transition

The effect of dielectric strengthening under electrical breakdown in thin oxide films and other materials is discussed. The breakdown phenomenon is considered as an insulator-to-metal phase transition. The effect of strengthening is thus associated with the fact that no phase transition seems to be possible when the system size is decreased below a certain characteristic length d _c (it is a so-called ‘tachyon instability’). This dimension is estimated to be d _c?～?ξ, where ξ is the correlation length for metal–insulator transition.