Time-dependent Newns-Anderson Model Research Articles

An interpolation formula for electron transfer in atom-surface collision and its validity

An interpolation scheme between fast and slow atom motion limits is presented based on the Mahanthappa-Baksi-Keldysh Green's function formalism for the time-dependent Newns-Anderson model. Its validity is examined for various limiting cases such as wide band limit, narrow band limit, slow atom-motion limit, and fast atom-motion limit. Various mathematically tractable models for time dependence and energy dependence for matrix elements appearing in the theory are employed. It is shown that the approximation is fairly good for most of the limits, but poor for the case in which an oscillatory behavior is observed in the charge fraction as a function of the atom velocity. It is also shown that the Landau-Zener tunneling theory must be modified when level crossing takes place and the atom motion is fast.

Charge states of sputtered atoms/ions

The charge states of sputtered cesium and oxygen ions/atoms from metal surfaces have been discussed with the time-dependent Newns-Anderson model. The final charge state distribution has been calculated as a function of work function of the surfaces. The calculated results fit the experimental data well. Besides, the dependence of the final charge states of the sputtered oxygen particles on the surface temperature is also predicted.

CALCULATION OF CHARGE EXCHANGE IN POTASSIUM IONS/ATOMS SCATTERED FROM METAL SURFACES

The charge-exchange processes of K ions/atoms scattered from metal surface are discussed in terms of the time-dependent Newns-Anderson quantum model with intra-atomic Coulomb interaction. The final charge-states distribution is calculated as a function of work function of the surfaces. The calculated results are compared with the experimental data. Furthermore, the probabilities of charge states of the moving K ions/atoms approaching to and leaving from the surface are demonstrated.

A short story of SIN!

A brief overview is given of the theory of surface-ion neutralization (SIN) by highlighting studies from the pioneering days to the present time. Emphasis is placed on the 1-electron time-dependent Newns-Anderson (TDNA) model, which has played such a key role in studying resonance charge transfer. Recently, a many-electron (ME) version of the TDNA approach has been formulated to treat two or more electron processes, such as Auger transitions. The equation-of-motion technique is used to obtain the TD coefficients from which the required SIN probabilities can be found. After outlining the ME method, two applications are described. The first deals with the Li +- Cs W (110) system, while the second addresses the laser enhancement of SIN, in the case of Li +-KBr, and revises some earlier results.

Calculation of charge-exchange in lithium ions/atoms scattered from cesiated metal surfaces

The charge states of Li ions/atoms scattered from a Cs/W(110) surface have been calculated as a function of work function and the temperature of surface in terms of the time-dependent Newns-Anderson quantum model with the intra-atomic Coulomb interaction. The calculated results are in good agreement with the experimental data. Furthermore, the probabilities of charge states of the moving Li ions/atoms approaching to and leaving from the surface are demonstrated.

Charge-exchange in cesium ions/atoms scattered or sputtered from metal surfaces

The charge states of Cs ions/atoms scattered from Cs/W(110) or sputtered from Cs/Al surfaces have been calculated as a function of the work function and the temperature of the surface in terms of the time-dependent Newns-Anderson quantum model with the intra-atomic Coulomb interaction. The calculated results are in good agreement with the experimental data. Furthermore, the probabilities of charge states of the moving Cs ions/atoms approaching and leaving the surface are demonstrated.

Angular distributions and charge exchange in Na scattering from clean and Cs covered Ag(111)

An experimental study of 35 eV Na scattering at normal incidence from a clean and Cs covered Ag(111) surface is presented. The measured ion and neutral yield are in quite good agreement with model calculations by Nakanishi et al. using the time-dependent Newns-Anderson model taking into account the Coulomb interaction between electrons of opposite spin occupying the ionization and affinity level. For a complete description local work function effects cannot be neglected. With the help of classical trajectory calculations most of the scattering phenomena can he understood, both for the clean and for the cesiated surface. From the measurements a neutralization cross section of 175 ± 40 Å 2 is extracted for each adsorbed Cs atom. The pronounced rainbow scattering observed for the clean surface is masked but does not disappear upon Cs adsorption.

Electron correlation effects on charge transfer and energy dissipation in atom or ion scattering from metal surfaces

The charge transfer and the energy dissipation in the scattering of a particle from a metal surface is investigated within the framework of the time-dependent Newns-Anderson model laying stress on the effects of the intra-atomic Coulomb interaction on the particle. The final energy distributions of the electronic system are calculated by the perturbational expansion with respect to the electron hopping matrix element between the particle and the metal surface. The numerical results up to the fourth order terms are presented for the hydrogen scattering from the tungsten surface.

Beam Kondo effect? — Possible anomalous penning deexcitation spectrum

It is shown that the Penning deexcitation spectrum of the triplet 2s excited helium atom beam at metal surfaces can have a threshold anomaly, which is the Kondo effect. The time-dependent Newns-Anderson model is used to analyze the transition rate of the deexcitation in the quasi-static approximation. The effect is due to the spin as well as potential scattering of conduction electrons by the He atom in the triplet excited state as the initial state interaction. Line shape of the Penning deexcitation spectrum is discussed, and clean surfaces of alkali metals are pointed out to be possible candidates to observe this many body effect.

Analytic approach to charge transfer during atom-surface scattering.

We present an analytic approach to the solution of the time-dependent Newns-Anderson model of charge transfer during atom-surface scattering. For sufficiently slow atomic velocities we show, using a WKB technique, that the time evolution of the electronic state of the atom is determined by the instantaneous quasiparticle energies of the coupled atom plus surface system. Surface electronic structure and level-crossing effects are thus incorporated into the theory in a natural way. The results of the analysis compare quite favorably with numerical solutions and recently discovered exact solutions.

Final energy distributions of the electronic system in atom or ion scattering from metal surfaces

The electronic energy transfer associated with the charge transfer in the scattering of particles from metal surfaces is investigated within the framework of the non-interacting time-dependent Newns-Anderson model in the wide-band limit. In this paper, the final energy distributions of the electronic system are shown to be decomposed into parts related to the initial as well as the final charge state of the particles (neutral atoms and positive ions). As a result of numerical calculations, several characteristic structures are found in the final energy distributions. Their origins are explained briefly.

Exact calculation for the time-dependent Newns-Anderson model in a small system: II. Scattering geometry

The charge transfer problem between metal surfaces and moving atoms is investigated in the time-dependent Newns-Anderson model. Exact numerical calculations are performed for a small system with 8 electrons in the scattering geometry of positive ion incidence. The intra-atomic Coulomb interaction is treated without approximations. The results are compared with those of the Hartree-Fock approximation. From the comparison, we see that the Hartree-Fock approximation provides rather good results for scattering to non-negative charge states, but for the fraction of negative ions, the electron correlation effect on the atom seems essential.

Exact calculation for the time-dependent newns-Anderson model in a small system

The charge transfer problem between metal surfaces and moving atoms is investigated in the time-dependent Newns-Anderson model. Exact calculations are performed for a small system with 8 electrons. The intra-atomic Coulomb interaction is treated without approximations. The results are compared with those of the Hartree-Fock approximation. From the comparison, we see that the Hartree-Fock approximation provides rather good results for the atom-velocity dependence except for its prefactor, but for the fraction of negative ion, the electron correlation effect on the atom seems essential.

Charge exchange scattering of particles from metal surfaces

The ionization probability of a particle scattered from a metal surface is investigated with the aid of the time-dependent Newns-Anderson model laying stress on the effects of the intra-atomic Coulomb interaction. Also, the relationship is investigated between the charge transfer and the various quantities such as the velocity of the particle, its initial probability of being charged, the work function and the temperature of the surface. A good account of the experimental data is given for the ionization of sodium atoms scattered from the W(110) surface.

Equation of motion method for the time-dependent Newns-Anderson model

The time-dependent Newns-Anderson model including the intra-atomic Coulomb interaction is investigated by means of the Heisenberg equation of motion. It is shown that a hierarchy of equations can be derived for the time-dependent expectation values of charged states for atoms moving near metal surfaces. A truncation procedure is used to reduce these equations to a closed form. A simple case of time-dependence for parameters in the model is examined numerically.

Equation of motion method for the time-dependent newns-Anderson model

Equation of motion method for the time-dependent newns-Anderson model

Correlation effects on charge exchange in the time-dependent Newns-Anderson model

The electron correlation effect on the charge exchange problem in the time-dependent Newns-Anderson model with U→∞ is discussed in the approach of the expanded wavefunction in terms of electron-hole pair excitation. Only a limited case is analyzed rigorously on the expansion terms up to the eighth order of the admixture coupling constant to conclude that the same expression holds for the non-adiabatic exchange of the total charge as in the non-interacting case. This conclusion is conjectured to hold somewhat generally.

Oscillation of the Spin Polarization in the Time-Dependent Newns-Anderson Model

The oscillatory approach in time to the equilibrium value of the spin polarization of moving atoms near metal surfaces is analyzed in detail, which appears in the Hartree-Fock approximation for the time-dependent Newns-Anderson model. The approximate asymptotic solution is obtained for the long time behavior of the spin polarization and also the detailed analytic property of the exact solution for long time is discussed.

Time-dependent Newns-Anderson model

The recent development is reviewed of the time-dependent Newns-Anderson model to describe the nonadiabatic effects due to moving particles such as atoms and molecules on metal surfaces. A brief sketch of the historical background is given and the foundation of the model is discussed such as the trajectory approximation and the time-dependence of parameters. The charge exchange, effects of the intraatomic Coulomb interaction and the energy dissipation are discussed, and some remarks conclude the article.