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.     

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.     

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.     

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.     

Direct recursion of the ratio of Bessel functions with applications to Mie scattering calculations

The primary goal of this paper is to describe a method to directly calculate the ratios between the Bessel functions of the first and second kind. This new method is introduced and discussed under the context of Mie scattering calculations. Past work on Mie calculations has mostly relied on calculating the Bessel functions separately, then taking the ratio. This technique fails when the order of the functions becomes appreciably larger than the argument. To solve this problem, we developed a stable method to directly calculate the ratio. When applied to Mie scattering calculations, the new method improves the control of the desired accuracy and enables calculations with higher precision. Since many other wave propagation problems also involve the ratios of Bessel functions and our method provides reliable and accurate calculations over a wide range of conditions, we expect it to find applications beyond Mie calculations.     

PDF calculations of piloted premixed jet flames

A series of piloted premixed jet flames with strong finite-rate chemistry effects is studied using the joint velocity-turbulence frequency-composition PDF method. The numerical accuracy of the calculations is demonstrated, and the calculations are compared to experimental data. It is found that all calculations show good agreement with the measurements of mean and rms mixture fraction fields, while the reaction progress is overpredicted to varying degrees depending on the jet velocity. In the calculations of the flame with the lowest jet velocity, the species and temperature show reasonable agreement with the measurements, with the exception of a small region near the centerline where products and temperature are overpredicted and fuel and oxidizer are underpredicted. In the calculations of the flame with the highest jet velocity, however, the overprediction of products and temperature and underprediction of fuel and oxidizer is far more severe. An extensive set of sensitivity studies on inlet boundary conditions, turbulence model constants, mixing models and constants, radiation treatment, and chemical mechanisms is conducted to show that any parameter variation offers little improvement from the base case. To shed light on these discrepancies, diagnostic calculations are performed in which the chemical reactions are artificially slowed. These diagnostic calculations serve to validate the experimental data and to quantify the amount by which the base case calculations overpredict reaction progress. Improved calculations of this flame are achieved only through artificially slowing down the chemical reaction by a factor of about 10. The mixing model behavior in this combustion regime is identified as a likely cause for the observed discrepancy in reaction progress.     

o-C8碳：新的超硬碳同素异形体

通过粒子群优化算法和密度泛函计算,证明了空间群为PMMA的正交晶系的碳同素异形体o-C₈是稳定的超硬相. 声子谱计算表明,o-C₈碳相是动力学稳定的;体积压缩计算表明,它是体模量为298.6 GPa的高度不可压缩材料. o-C₈相是一种新型的密度为2.993 g/cm³、维氏硬度为67.0 GPa的低密度超硬材料.     

Treatment of continua in the shell-model theory of nuclear reactions

It is shown that by a suitable choice of the bound- and continuum-state functions used to perform shell-model calculations, the continuum-continuum interaction may be minimized. Approximate expressions for the scattering matrix elements are derived that are easily evaluated by simple extensions of the conventional shell-model calculations for bound states. Numerical calculations are performed for neutron scattering from ¹²C within the framework of the deformed rotor model and compared with exact coupled-channel calculations.     

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.     

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.     

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.     

An efficient numerical method for time-dependent NLTE radiation transfer

We present a numerical method for performing coupled time-dependent radiation transfer and atomic rate equation calculations. The method incorporates the desirable features of time-dependent, non-local thermodynamic equilibrium (NLTE) radiation transfer calculations. It has the advantage that it allows existing time-dependent calculations to be adapted to model time dependent effects. The approximations which are used are discussed.Calculations have been performed for a highly ionised silicon plasma with a single optically thick line. The line is taken to have a top-hat profile which is independent of position. Although the model is simple, it serves to illustrate some important features of time-dependent calculations.     

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.     

Computational study of lean premixed turbulent flames using RANSPDF and LESPDF methods

A computational study is performed on a series of four piloted, lean, premixed turbulent jet flames. These flames use the Sydney Piloted Premixed Jet Burner (PPJB), and with jet velocities of 50, 100, 150 and 200 m/s are denoted PM150, PM1100, PM1150 and PM1200, respectively. Calculations are performed using the RANSPDF and LESPDF methodologies, with different treatments of molecular diffusion, with detailed chemistry and flamelet-based chemistry modelling, and using different imposed boundary conditions. The sensitivities of the calculations to these different aspects of the modelling are compared and discussed. Comparisons are made to experimental data and to previously-performed calculations. It is found that, given suitable boundary conditions and treatment of molecular diffusion, excellent agreement between the calculations and experimental measurements of the mean and variance fields can be achieved for PM150 and PM1100. The application of a recently developed implementation of molecular diffusion results in a large improvement in the computed variance fields in the LESPDF calculations. The inclusion of differential diffusion in the LESPDF calculations provides insight on the behaviour in the near-field region of the jet, but its effects are found to be confined to this region and to the species CO, OH and H₂. A major discrepancy observed in many previous calculations of these flames is an overprediction of reaction progress in PM1150 and PM1200, and this discrepancy is also observed in the LESPDF calculations; however, a parametric study of the LESPDF mixing model reveals that, with a sufficiently large mixing frequency, calculations of these two flames are capable of yielding improved reaction progress in good qualitative agreement with the mean and RMS scalar measurements up to an x/D of 30. Lastly, the merits of each computational methodology are discussed in light of their computational costs.     

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.     

Examination of high-throughput hybrid calculations using coarser reciprocal space meshes

High-throughput density functional theory calculations have been typically performed with reduced accuracy and notable error in the band gap. Here we suggest several approaches to calculate the optoelectronic properties by using coarser k-point meshes for the Fock exchange potential. In our benchmark calculations, we were able to obtain the optical properties of zinc-blende and wurtzite materials with reasonable accuracy. We also propose an approach of high-throughput calculations using a pre-converged wavefunction by the reduced k-point meshes for the Fock exchange and performing the subsequent non-self-consistent-field calculations.     

CO on Pd(110): determination of the optimal adsorption site

We present ab initio pseudo-potential plane-wave total-energy calculations for the geometric and electronic structure of the CO-covered Pd(110) surface. Our calculations were performed within the local-density approximation (LDA) of density functional theory (DFT). There has been some controversy as to whether CO prefers to adsorb at a bridge or on-top site when exposed to Pd(110). Total energy calculations for a CO monolayer adsorbed at the on-top and bridge adsorption sites revealed the bridge site adsorption to be favored by 0.59 eV per CO molecule. The preferential adsorption of CO to the bridge site was further corroborated by our band-structure calculations, with only the bridge site results being in good agreement with recent inverse photoemission experiments.     

Zero momentum calculations for finite temperature field theory

Problems with calculations of Feynaman diagrams with no external leg carrying non-zero momentum for a finite temperature scalar field theory using a real time path integral approach are considered. The necessary extra rules for all such calculations are derived, covering all the usual methods of calculating the effective potential, and several problems with such calculations from the path integral viewpoint are resolved.     

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.     

Difficulties in applying pure Kohn-Sham density functional theory electronic structure methods to protein molecules

Self-consistency-based Kohn-Sham density functional theory (KS-DFT) electronic structure calculations with Gaussian basis sets are reported for a set of 17 protein-like molecules with geometries obtained from the Protein Data Bank. It is found that in many cases such calculations do not converge due to vanishing HOMO-LUMO gaps. A sequence of polyproline I helix molecules is also studied and it is found that self-consistency calculations using pure functionals fail to converge for helices longer than six proline units. Since the computed gap is strongly correlated to the fraction of Hartree-Fock exchange, test calculations using both pure and hybrid density functionals are reported. The tested methods include the pure functionals BLYP, PBE and LDA, as well as Hartree-Fock and the hybrid functionals BHandHLYP, B3LYP and PBE0. The effect of including solvent molecules in the calculations is studied, and it is found that the inclusion of explicit solvent molecules around the protein fragment in many cases gives a larger gap, but that convergence problems due to vanishing gaps still occur in calculations with pure functionals. In order to achieve converged results, some modeling of the charge distribution of solvent water molecules outside the electronic structure calculation is needed. Representing solvent water molecules by a simple point charge distribution is found to give non-vanishing HOMO-LUMO gaps for the tested protein-like systems also for pure functionals.