Atom Model Potential Research Articles

Three-photon ionization of lithium

Abstract We study three-photon ionization of neutral lithium, in the presence of a strong laser light intensity of up to 15 GW cm −2 , involving the absorption of three photons combined in such a way that first we have one-photon resonant plus two-photon non-resonant ionization transitions, then the reverse case is studied. The resolvent operator formalism and projection operators are used in the calculations. An atomic central field model potential is used to generate orbital wavefunctions. We compare our calculations with previous calculations done by Chang and Poe [Phys. Rev. A 16 (1977) 606] for non-resonant three-photon ionization rates of lithium, with which we obtained a very good agreement.

Positions and widths of anticrossings due to FS interaction for K Rydberg - Stark states

With wavefunctions from a kind of atomic potential model including the fine-structure (FS) interaction as a basis, we calculate the positions and widths of anticrossings due to the FS interaction for the case of K Rydberg states in a static electrical field by using the diagonalization method. The results are in good agreement with experimental data; and we confirm that the influence of the FS interaction is very small on anticrossing brought about by core interaction. The accuracy of the potential model wavefunction including the FS interaction is sensitively and numerically tested in the situation of external fields.

Positions and widths of anticrossings for Cs Rydberg Stark states

With wavefunctions from a kind of atomic potential model as a basis, we calculate the positions and widths of anticrossings for the case of Cs Rydberg states in a static electrical field. The results are in excellent agreement with experimental data and somewhat better than other theoretical ones. The accuracy of the potential model is further sensitively and numerically tested, especially through comparing theoretical widths with experimental ones. We also discuss the influence of the zero-field radical wavefunctions truncated near the core on the position and width of anticrossing, and we find that there is almost no influence on the position and width of anticrossing when the cutoff radii are taken from zero to 10.24 a.u. in the states concerned in this paper.

Predicted carbon-cluster field evaporation from graphite by pulsed-field STM

Field evaporation of carbon as positive and negative ions from the clean graphite (001) plane surface under STM pulsed-field conditions has been investigated. We use the charge-exchange model, taking the potential from a simple empirical atomic potential model. The removed carbon atom considered here initially resides in the perfect graphite surface, rather than being an adsorbed atom. Assuming a clean tungsten tip as counterelectrode, threshold electric fields for C −, C +, and C 2+ have been obtained. We further consider the possibility of field evaporation of C clusters. Our calculations indicate that C atoms can field-evaporate as members of ionic clusters at much lower threshold fields than a single carbon atom can. We conclude that ionic carbon clusters are favored in field evaporation from graphite, based on lower threshold fields obtained in the charge-exchange model.

Microwave multiphoton transition of the Rydberg potassium atom

By using the Floquet method plus a kind of atomic potential model, we directly calculate the multiphoton transition probability of Rydberg potassium in strong microwave fields. For the first time we give multiphoton resonance spectra that can be compared with experimental ones. According to the viewpoint of a multi-step or rate-limiting step about microwave ionization, our method can be used to quantitatively study multiphoton ionization processes.

Molecular dynamics studies of self-interstitials in ice Ih

We carried out molecular dynamics simulations of interstitial water molecules in ice to clarify behavior and vibrational properties of self-interstitials in ice. We used an atom–atom potential model developed by Kumagai et al. [N. Kumagai, K. Kawamura and T. Yokokawa, Mol. Sim. 12, 177 (1994)] which allows intramolecular motions. We confirmed high reliability of the potential model for reproducing the structure and vibrational spectra of ice. From trajectory observations of self-interstitials, we found that a stable interstitial site is an uncapped trigonal site. By comparing power spectra of vibrational motions for self-interstitials with that of matrix ice, we found that the large formation entropy of the interstitial molecule is attributed to much higher density of states in a low frequency region for the interstitial than that for the matrix.

Vibration and rotation of CO in C60 and predicted infrared spectrum

We present the Hamiltonian for the vibrations and rotations of CO inside a freely rotating or fixed C60 molecule and we calculate its eigenstates from an atom–atom model potential. The ensuing level structure can be understood in terms of three basic characteristics. (i) Simultaneous rotations of CO and its position vector R, which give rise to a rotational structure similar to that of free CO. The effective rotational constants differ considerably, however. (ii) Splittings of the levels by the icosahedral field of C60 which perturb the regular rotational structure, because they are of the same order of magnitude as the rotational spacings. (iii) Large frequencies associated with the (nearly harmonic) vibrations of CO against the hard walls of the C60 cage: 209 cm−1 for the radial excitation and 162 cm−1 for the twofold degenerate libration. These vibrations give a rovibrational level structure similar to that of a linear triatomic molecule, the radial excitation resembles a bond stretch (Σ) state, the libration a Π-bending state. From the eigenstates we calculate the line strengths of the electric dipole transitions allowed by the icosahedral symmetry. Additional (approximate) selection rules are found, and the infrared spectrum of CO&at;C60 is predicted.

Inner-shell capture using atomic potentials: A distorted strong-potential Born treatment.

The influence of a distorted nuclear motion on electron capture from the inner shells of atoms, when atomic model potentials, rather than scaled Coulomb potentials, are used in the motion of the active target electron, is investigated in the distorted strong-potential Born approximation to the exact capture amplitude. A comparison is made with the earlier undistorted strong-potential Born approximation and other theories, and with experiment. The modification of the impulse-approximation cross section is shown to be generally much less in the distorted theory and is shown to give quite good agreement with the experimental data. At energies below the peak in the capture cross sections, the present results show significantly better agreement with experiment and also good agreement with the recent coupled-Sturmian-pseudostate results of Winter [Phys. Rev. A 47, 264 (1993)], who used the same atomic model potential.

An EAM simulation of the alpha - gamma iron interface

The embedded atom method was used for the design of an atomic potential model for the simulation of the alpha - gamma iron interface. The model takes the form of three cubic expressions covering different ranges, and is normalized to give equilibrium to the two-body potential as well as to the embedding function at the perfect lattice configurations of both the alpha and gamma phases. The model yields good results for surface energies and the vacancy formation energy. Simulations were carried out for alpha - gamma interfaces with the Nishiyama-Wasserman orientation relationship. Interface energies were calculated for interfaces without structural ledges, with monoatomic ledges and with triatomic ledges with results close to the experimental values. The relaxation behaviour of the lattices from their initial configurations was also studied, and it was found that most of the relaxation occurs along the atomic habit planes instead of perpendicular to them. No major effect of different boundary conditions on the lattice relaxation and the interface energy was observed.

Comment on 'Bifurcation behaviour in structural phase transitions with multi-well potentials'

For original work see ibid., vol.2, no.16, p.3737 (1990). Normand and co-workers predicted anomalous temperature dependence of a few thermal averages induced by the bifurcation behaviour or the local breaking of symmetry. Against their prediction, based on the phi 4 atom potential model, the double-quadratic-well (DQW) potential model leads to different temperature dependences on the specific heat and the mean square displacement. It turns out that the anomalous temperature dependence of the phi 4 model arises from the anharmonic character of the potential barrier as well as the bifurcation behaviour. Making a distinction between the two kinds of anomaly, the authors present a plausible temperature variation of the bifurcation behaviour on the basis of the DQW model of the above two quantities.

Effective radiative recombination coefficients of atomic oxygen

Effective radiative recombination coefficients are calculated for atomic oxygen using an atomic model potential to obtain accurate non-hydrogenic transition probabilities of singly excited states. Results are presented for many lines for temperatures up to 3000 K. Simple analytic fits are given which are accurate for most lines.

Effective recombination coefficients of neutral carbon and singly ionized nitrogen

view Abstract Citations (50) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effective Recombination Coefficients of Neutral Carbon and Singly Ionized Nitrogen Escalante, Vladimir ; Victor, G. A. Abstract Effective recombination coefficients were calculated for neutral carbon and singly ionized N lines using an atomic model potential to obtain accurate nonhydrogenic transition probabilities and recombination cross sections of singly excited states. Published nonhydrogenic data for two-electron transitions and dielectronic recombination coefficients were used to complete the calculation of the cascade. The tabulated coefficients are given as a function of temperature and can be used to calculate the emissivity of recombination lines of transitions from levels with n less than 8 and l less than 3. Total recombination coefficients are also given. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1990 DOI: 10.1086/191479 Bibcode: 1990ApJS...73..513E Keywords: Atomic Recombination; Carbon; Ionized Gases; Nitrogen Ions; Recombination Coefficient; Forbidden Bands; Heavy Elements; Line Spectra; Radiative Recombination; Atomic and Molecular Physics; ATOMIC PROCESSES; TRANSITION RATES full text sources ADS |

Wavefunctions and oscillator strengths of high Rydberg alkali atoms by a simple atomic potential model

The analytical wavefunctions and oscillator strengths between highly excited states of alkali atoms over a wide range of principal quantum number n(10<or=n<or=40, and for Na, n<or=60) are calculated straightforwardly by using a simple, one-parameter, exactly soluble model for atoms. The valence electron of the atom is assumed to be in a potential of the following form: V(r)=-e/r1+ delta + alpha '/r+ gamma '+ beta '/(r+ gamma ')2 where alpha ', beta ', gamma ' are the parameters to be determined and delta is the ionicity. Analytical solutions can be obtained by solving the Schrodinger equation containing V(r). The parameters in the potential and the wavefunction, which are dependent on the atomic states, can be expressed in terms of a single parameter, the quantum defect. The wavefunctions of the alkali atoms were obtained, and their general behaviour and the number of nodes agree with Hartree-Fock-Slater theory. This model is well suited for studying the behaviour of atoms that are mainly dependent of the outer region of high Rydberg states.

WAVE FUNCTIONS FOR AND OSCILLATOR STRENGTHS BETWEEN HIGH RYDBERG STATES OF Na ATOM

摘要 用我们提出的一种具有解析解的原子唯象势模型, 计算了Na原子里德伯态(10≤n≤40)的波函数和ns--n'p ,np--n'd, nd--n'f 高里德伯态间的振子强度, 与以方法得到的结果很接近. 计算结果表明, 上述振予强度满足某种标度律. Abstract The phenomenological atomic potential model with analytical solutions is employed to obtain the wave functions of the Rydberg states (10≤n≤40) and the oscillator strengths of the ns--n'p ,np--n'd, and nd--n'f transitions between them. The results are very close to those obtained by the CA method. These results show that there exists a kind of sealing law for the above oscillator strengths. 作者及机构信息 李白文；陈暖球；张学荣；张承修 1. 中国科学院武汉物理研究所波谱与原子分子物理开放研究实验室 Authors and contacts Li Wen-bai Chen Nuan-qiu Zhang Xue-rong Zhang Cheng-xiu 参考文献 施引文献

Optical oscillator strengths for the phosphorus isoelectronic sequence

An analytic atomic independent-particle model potential, adjusted to experimental single-particle energy levels, is used to generate wave functions for the valence and excited states of P, S+1, Cl+2, Ar+3, K+4, and Ca+5. Using these wave functions in conjunction with the Born approximation and the LS-coupling scheme, we calculate optical oscillator strengths for excitations from the ls22s22p63s23p3(4S3/2) ground state. Reasonable agreement is obtained with available experimental and theoretical data.

Atomic and molecular model potentials

A constructive theory of atomic and molecular model potentials is developed using the work of Bottcher and Dalgarno as a point of departure. In this theory, all of the terms required by successful, empirical, model potential calculations are obtained from a perturbation theory in which exchange is neglected. We find that valence electrons must be allowed to penetrate into the core regions even in systems with well defined cores and distant valence electrons. Within this theory, exact model potentials for hydrogenlike atoms and H2-like molecules are obtained and specific, short- and long-range forms of the model potentials are proposed for other atoms and molecules.

Use of atomic fues potential within the floating spherical gaussian orbital method: Study of some two-valence-electron diatomics and triatomic ions

Atomic Fues potential type model potential is used within the floating spherical gaussian orbital formalism to study a series of two-valence-electron diatomics and triatomic ions. Calculated equilibrium geometries and force constants are in excellent agreement with available experimental data and results of all-electronab initio studies. Electron populations are given for fourteen diatomic species and comparison has been made with the results of other theoretical studies. The predicted results are generally satisfactory.

An Investigation of Atomic Model Potentials Soluble in Closed Form

An Investigation of Atomic Model Potentials Soluble in Closed Form

A Pseudopotential Approach to the Structure of As

The internal energy of As crystal is investigated as a function of structure parameters and volume in terms of the pseudopotential expansion method. An atomic model potential derived from Lin and Falicov's one is used. Calculations in second order approximation explain successfully the stability of the unusual A7 structure of As, the temperature dependence of structure parameters, and pressure-induced phase transformation from A7 to simple cubic, but give rise to unusual results in conflict with experimental facts with respect to large volume change. The third order contribution does not improve the situation. It is discussed that these shortcomings are attributed to the truncated nature of Lin-Falicov's potential.

Exact one-electron eigenenergies for a class of atomic model potentials

Exact one-electron eigenvalues are computed for a class of potentials which consist of a constant step and of a Coulomb tail, and include as particular cases several models for atomic potentials extensively used in the applications. Some general properties of these potentials are discussed, with particular reference to their suitability to describe alkali atoms.