Model Potential Technique Research Articles

A revised study of the [formula omitted] alkali-dimer using a model potential approach

The model potential approach is well adapted to study atomic and molecular systems involving a single active electron. Such is the case of the alkali-dimer lithium cation Li2+. However, a comparison of the model potential results of Magnier et al. (1999) and those based on ab initio techniques (Bouzouita et al., 2006; Jasik et al., 2007, Musial et al., 2015) raises a number of questions related to the existence of an important disagreement regarding several excited states,which are found to be repulsive by Magnier et al. (1999) but attractive when ab initio techniques are employed.In this paper, we propose to re-investigate the Li2+ system, using a model potential technique to compute the adiabatic energy curves and the molecular spectroscopic constants. Our aim is to clarify whether this disagreement between the ab initio and model potential methods originates from some conceptual defect of the model potential technique or whether there is some source of error in the calculations of Magnier et al. (1999).

Calculations of dynamic dipole polarizabilities of Li and Na atoms in debye plasma using the model potential technique

The effects of Debye plasma on the frequency-dependent polarizabilities of Li and Na atoms are investigated using symplectic algorithm within the framework of the pseudostate summation technique. Dynamic dipole polarizabilities of Li (2s 2S) and Na(3s 2S) as functions of scaled number density of the plasma electrons for arbitrary plasma temperature are presented. Screening effects on the resonance frequencies are also presented. In free-atomic cases, our calculated results are comparable with the reported theoretical and experimental predictions. © 2012 Wiley Periodicals, Inc.

A model potential technique for the calculation of the band structure of poly(glycine)

The application of a model potential technique for calculating band structures of polymers is described. In this approach, the valence Hamiltonian is a sum of a kinetic term and of various effective atomic potentials chosen in a nonlocal form of Gaussian projectors. Results are given for poly(glycine) I (parallel and antiparallel).

A nonempirical model potential technique for calculations of band structures of polymers

The application of a model potential technique for calculating band structures of polymers is described. In this approach, the valence Hamiltonian is a sum of a kinetic term and of various effective atomic potentials chosen in a nonlocal form of Gaussian projectors. Actual results on polyethylene and polyacetylene (infinite polyene) are given.

Model Potential Approach to Core Polarisation in SCF Calculations

The paper discusses the applicability of simple model potentials used to describe the valence-core electron correlation (core polarisation in a semiclassical picture) within fully relativistic self-consistent-field Dirac-Fock calculations. The influence of core polarisation on oscillator strengths is demonstrated for medium and heavy systems with one and two valence electrons and is compared with other correlation effects (e.g. intravalence correlation), where applicable. Different forms of core polarisation potential and induced transition dipole moment are presented and discussed, together with limitations of the core polarisation picture. Though the emphasis is on the use of core polarisation potentials within SCF calculations, these potentials are also widely employed within a valence electron effective model potential approach. Some recent results obtained with different effective model potentials for Ag and Au isoelectronic sequences are presented and compared with SCF calculations. Finally, our earlier results obtained with the core polarisation picture are compared with the most recent unpublished results where the valence-core electron correlation (core polarisation) is explicitly represented in the configuration interaction (CI) scheme and spin-orbitals are generated by employing an ab initio model potential technique with noninteger outermost core shell occupation number, intended to improve the efficiency of the CI representation of the valence-core correlation.

Collisions between multiply charged ions The He 2+C 3+ case

Total cross sections for single charge transfer in 3He 2+ 13C 3− collisions are calculated in the 2–200 keV centre of mass energy range within the molecular approximation. Model potential techniques are used to determine the adiabatic energies and the nonadiabatic coupling matrix elements. The collision dynamics are then treated by the semiclassical impact-parameter approximation with allowance for translation factors. The reliability of straight-line nuclear trajectories is asserted by fully quantum mechanical test calculations. Comparison is made with recent experimental results.

Model potential methods for the description of electron capture by multiply charged ions from single and multi-electron targets: Application to Ar6+–H and Ar6+–He systems

It is demonstrated how model potential methods can be adapted to generate an adiabatic basis set for the description of single electron capture by multicharged ions from many-electron targets. The calculated curve-crossing parameters are compared with other semi-empirical estimations. The sensitivity of the electron capture cross sections to these parameters is discussed with reference to the Ar6+–H and Ar6+–He systems. The comparison with experimental data for the Ar6+–He system indicate that model potential techniques are very satisfactory. For the Ar6+–H system, a detailed interpretation of the experimental energy gain spectra is difficult because of the strong overlap of the electron capture channels. A quantitative comparison with the two-centre atomic state basis set calculations reveals some significant discrepancies in the forward scattering of the 5s capture channel.

Calculations on the Quartet Spectrum of B III

A model-potential technique is used to calculated wave functions and energy eigenvalues for quartet levels of B III. Transition wavelengths and probabilities, oscillator strengths and radiative decay lifetimes are presented. Some assignments which have been proposed for lines observed in beam-foil spectra of boron are confirmed but it is suggested that some lines have been incorrectly classified.

Application of model potential method in calculating Rydberg states of rare-earth elements Tm, Yb, Lu and their ions

Asymptotically precise calculations have been carried out with n to infinity , for the Rydberg states 4f136sns of the Tm atom, the 4f146sns, 4f146snp states of the Yb atom and the Lu+ ion, the 4f14ns, 4f14np, 4f14nd states of the Yb+ and Lu2+ ions and the 4f146s2ns, 4f146s2np, 4f146s2nd states of the Lu atom. The Lu atom and Yb+ and Lu2+ ions are considered as a system with one electron above the core of the closed shells 4f146s2 or 4f14. The Yb atom and Lu+ ion are regarded as a system with two electrons above the core. The Tm atom is considered as a system with 4f-1 vacancy and the 6s, ns electrons above the 4f14 core. In calculating energies with one electron above the core the energy is extrapolated as a function of the principal quantum number n by the model potential technique. The potential constructed at this stage is used as a zero-order approximation in calculating states with two and three quasiparticles (vacancies and electrons) above the core. The corrections for the energies of the states of two- and three-quasiparticle systems are calculated with the use of the perturbation theory. The first order has been allowed for completely. In the higher orders effective allowances have been made for the corrections which with n to infinity make contributions of approximately 1/n3. Consideration is given to the non-Coulomb features of Rydberg spectra not vanishing within n to infinity .

Model potential calculations on open-shell molecules

It is shown that the model potential techniques used for systems with closed-shell cores can be extended to open-shell cores without difficulty. The method is applied to calculate potential energy curves for the molecules HeH+ and He2+. The results are in good agreement with ab initio calculations. Some interesting long-range curve crossings in HeH+ are discussed.