Collisions of electrons with molecules in excited vibrational-rotational states

Results are presented of calculations of cross sections for scattering of electrons by diatomic molecules in specific excited vibrational-rotational states. The calculations were made using an approximation based on a quantum theory of scattering in a system of several bodies which can be applied to calculations of direct reactions and reactions involving the formation of an intermediate transition complex. Results of calculations of cross sections for collisions of electrons with hydrogen, nitrogen, lithium, sodium, and hydrogen halide molecules are compared with existing experimental data and the results of calculations made by other authors.     

Fermi surface characteristics and enhancement factors for tantalum

We present calculations of the extremal areas of Fermi surface orbits in the bcc transition metal tantalum usingab initio linear muffin tin orbital method in the atomic sphere approximation. The calculations demonstrate the need to include relativistic corrections for a good representation of the Fermi surface. Self-consistent calculations are performed using various exchange-correlation potentials. The calculations indicate that Barth-Hedin-Janak exchange provides the best agreement with the experiment. Enhancement factors are also calculated using the BHJ exchange-correlation potential. These are compared with experimental results as well as with some of the available theoretical calculations.     

Effects of vortices in two-dimensional micromagnetic calculations

Smoothing errors in micromagnetic calculations compute infinite energy for vortices. In numerical calculations their energy is finite but the wrong value. In variable meshes the increasing energy with resolution produces artifacts into these calculations. This paper presents corrections for these problems.     

Conformational Analysis of 1,2-Dichlorobutane

Vibrational spectra have been published and normal coordinate calculations have been made for 1,2-dichlorobutane.^1,2 Those calculations were limited to the three conformers that had all four carbon atoms coplanar. Molecular mechanics calculations have now shown a conformer that was omitted to be the second most abundant conformer. Therefore, normal coordinate calculations have been made for this conformer and molecular mechanics calculations have been made for all possible conformers.     

Meson exchange contributions to electron-3He scattering

Theoretical calculations have been done corresponding to Ω-, σ-, π°-meson exchange between pairs of nucleons in ³He for e-³He inelastic scattering and compared with the experimental data for 14.6 GeV incident electrons. The purpose of these calculations was to see if these calculations could account for the experimental cross sections on either side of the quasi-elastic peak, where the impulse approximation calculations gave results less than 10% of the experimental cross sections. Meson exchange calculations account impressively for the experimental cross sections on the left side of the quasi-elastic peak, whereas the contribution of the meson exchange calculations on the right side of the quasi-elastic peak was found to be negligible.     

Terahertz investigations on photoisomerisable compounds

We performed computational terahertz studies on organometallic photoisomerisable compounds, employing both gas phase and solid phase calculations. The calculations demonstrate the potential of employing terahertz techniques on photoisomerisable compounds. In particular, the trans-ligand, counterion and crystal effects are evaluated via the density functional theory calculations. In order to fully understand the terahertz responses of the photoisomerisable compounds, their experimental terahertz spectra were obtained and compared to the calculations. The calculated spectra generally predict the experimentally observed absorption peaks, while combined gas phase and solid phase calculations offer better agreement with the experiments. The first principles calculations also reveal the sensitivity of terahertz signal on the photoisomerisation processes, suggesting a photo-terahertz set-up that could be built in the future to fast screen and fully understand the photoisomerisable compounds, for related applications such as photo-transducer and photo-switch that require photoinduced geometrical changes.     

Aluminum Hugoniot from model calculations including semicore electrons based on density functional theory

We present a method to obtain Hugoniot from model calculations based on density functional theory, and apply the method to aluminum Hugoniot. Technological advances have extended the experimental research of high energy density physics, and call for quantitative theoretical analysis. However, direct computation of Hugoniot from density functional theory is very difficult. We propose two step calculations of Hugoniot from density functional theory. The first step is molecular dynamics simulations with an ambient temperature for electrons. The second step is total energy calculations of a crystal with desired high temperatures for electrons and with the ambient temperature for electrons. We treated the semicore 2s and 2p electrons of aluminum as valence electrons only for the total energy calculations of the aluminum crystal. The aluminum Hugoniot from our model calculations is in excellent agreement with available experimental data and the previous density functional theory calculations in the literature.     

Editorial: Challenges and solutions in GW calculations for complex systems

We report key advances in the area of GW calculations, review the available software implementations and define standardization criteria to render the comparison between GW calculations from different codes meaningful, and identify future major challenges in the area of quasiparticle calculations. This Topical Issue should be a reference point for further developments in the field.     

Self-consistent LDA calculation in ion neutralization at metal surfaces

The neutralization of He⁺ scattered off aluminum is calculated via a self-consistent LDA where the metal surface is modeled by an LDA jellium surface, and its structure factor is consistently calculated. This approach includes Auger and plasmon-assisted neutralization channels of He⁺ to the He ground state in front of aluminum. We analyze these neutralization channels, which leads us to a revision of the usual calculations of ion neutralization on surfaces depending on the transferred energy lying below, near, or above the metal plasma frequency. The results of this calculation are compared with those of other methods, namely usual unscreened calculations, calculations which extrapolate bulk results, calculations performed for a step potential surface, and surface calculations in the long-distance limit.     

Molecular structure calculations applied to solid state polymer physics: Part I

This review focuses upon the applications of molecular structure calculations to determine the three-dimensional physicochemical features of polymeric solids. In some cases, the structure calculations are used to evaluate expressions arising from specific models or theories. As such, molecular structure calculations are auxillary aides in the illumination of the solid-state properties of polymers.     

Exact treatment of pairing correlations in Yb isotopes with covariant density functional theory

The effects of pairing correlation in Yb isotopes are investigated by covariant density functional theory with pairing correlations and blocking effects treated exactly by a shell model like approach(SLAP). Experimental one- and two-neutron separation energies are reproduced quite well. The traditional BCS calculations always give larger pairing energies than those given by SLAP calculations, particularly for the nuclei near the proton and neutron drip lines. This may be caused because many of the single particle orbits above the Fermi surface are involved in the BCS calculations, but many of them are excluded in the SLAP calculations.     

Spectroscopic and magnetic mirages of impurities in nanoscopic systems with focusing properties

We study the behavior of magnetic impurities in nanoscopic systems with focusing properties. In this paper, we analyze the spectroscopic and magnetic properties of Kondo, intermediate valence and magnetic impurities on a sphere with a metallic surface. Using exact calculations, we obtain important spectroscopic and magnetic mirages at the antipodes of the impurity location. When compared with calculations performed using effective models our results validate previous calculations of spectroscopic mirages. These calculations can be extended to other systems with focusing properties like quantum corrals where a similar behavior is expected.     

Effect of 0h11/2 Level on Shell Model Calculations of ^105Sb and ^107Sb

The full and reduced shell model calculations have been carried out for the light odd-even ^105Sb and ^107Sb isotopes. The model space has been chosen as 1d5/2, 0g7/2, 1d3/2, 2s1/2, and 0h11/2 for the full calculations and excluded 0h11/2 for the reduced calculations. The reduced shell model calculations of ^105Sb and ^107Sb isotopes are presented for the first time. We obtain the energy spectra for the ^105Sb and ^107Sb isotopes in the full and reduced model space by using CD-Bonn two-body effective nucleon-nucleon interaction. The resulting energy spectra are compared to the experimental results to understand the effect of the 0h11/2 level on the shell model calculations. We draw conclusions about the right model space in the shell model calculations for the isotopes around the N =Z= 50 region of the periodic table.     

The Coulomb capture of negative muons by hydrogen atoms in the non-adiabatic close-coupling approximation

We present some results obtained within the non-adiabatic close-coupling approximation for Coulomb capture during collisions of slow negative muons with hydrogen atoms. The calculations are performed in momentum-space and a statistical distribution analysis is used to obtain the final cross sections. The present model results are in harmony with existing calculations. We conclude that further calculations within the present approach are justified.     

A New Pseudospectral Method for Calculations of Hydrogen Atom in Arbitrary External Fields

A new pseudospectral method was introduced to calculate wavefunctions and energy levels of hydrogen atom in arbitrary potential.Some results of hydrogen atom in uniform magnetic fields were presented,high accuracy of results was obtained with simple calculations,and our calculations show very fast convergence.It suggests a new method for calculations of hydrogen atom in external fields.     

A simple shell model calculation of differential ionic relaxations at the (100) surfaces of NaCl structure alkali halides

The rumpling of anions and cations in the (100) surface layer of various rockSalt-structure alkali halides has been calculated using a simple extension of an original model due to Verwey. It is shown that reasonable agreement with the results of more sophisticated calculations can be obtained when the interionic potentials used in the calculations are derived from shell model calculations based on the elastic properties of the various materials. The idea of a “Surface ionic polarisability” is proposed, and the results of its use in rumpling calculations compared with those obtained using conventional “bulk” polarisabilities.     

Study of parameters of the angular distribution of photoelectrons in the relativistic quadrupole approximation

Relativistic calculations of differential cross sections for photoionization are performed and the behavior of parameters β, γ, and δ describing the angular distribution of photoelectrons in the quadrupole approximation is studied. The calculations were carried out for a number of atoms for kinetic energies of photoelectrons E _k ≈50 000 eV. The electronic wave functions of the initial and final states are calculated by the Dirac-Fock method taking into account the exchange interaction and a hole produced in the atomic shell upon photoionization. The dependence of parameters β, γ, and δ on the physical assumptions used in the calculations is studied. Comparison with nonrelativistic calculations shows that relativistic values of the nondipole parameters γ and δ can be substantially different even at low energies of photoelectrons. Our calculations of nondipole parameters γ and δ for the 2p-shell of the Kr atom better agree with the recent experimental data than nonrelativistic calculations performed earlier taking approximately into account the exchange interaction and neglecting a hole.     

Simulation of Spin-3/2 Blume-Capel Model on a Cellular Automaton with Heating and Cooling Algorithm

The spin-3/2 Blume-Capel model is studied using the heating and cooling algorithms improved from the Creutz cellular automaton (CCA). The calculations are done on various sizes of the simple cubic lattice in the 0≦D/J≦5 parameter region. The phase diagram of the model and temperature variation of the thermodynamic quantities are obtained. We confirm the existence of a critical end point within the heating calculations. However, in contrast to the heating
calculations, we do not obtain the first-order line at low temperature with cooling algorithm calculations. The results are compared with those of other theories.     

Hot and cold,nuclear and neutron matter

We report variational calculations of the equation of state of hot and cold, nuclear and neutron matter. The calculations cover a wide density range of interest in heavy-ion collisions and astrophysics. The “hot” calculations are limited to temperatures less than 20 MeV. A realistic nuclear hamiltonian that contains two- and three-nucleon interactions and fits the nucléon-nucléon scattering, as well as nuclear matter data, is used. Neutron star structure calculations are reported and their sensitivity to the three-neutron interactipn is examined. The liquid-vapor phase equilibrium, as well as the behavior of the effective mass in nuclear matter is discussed.