Calculation of ground state surface properties of simple metals including non-local effects of the exchange and correlation energy

The energy density functional formalism is used to calculate the ground state surface energies and work functions for simple metals. Non-local corrections to the exchange and correlation energies were included by means of a gradient expansion in the density. Good agreement is obtained with experiment.     

Polarization and exchange in electron scattering by atoms in solids

Two corrections are employed to the theoretical calculations of the cross-sections of elastic scattering of electrons by atoms in solids. The corrections are due to target polarization and electron exchange, of which the exchange is found to be more significant in the range of incident energies 100 to 1000 eV. Both the corrections are introduced through model potentials, for Li atoms as well as Al atoms in the solid state.     

Infinite order radiative corrections and renormalization

By means of the Ward identity and the correlation expansion derived earlier, we calculate virtual radiative corrections to an infinite order. Partial factorization of the correlation effects, as in the simple exchange processes, makes infinite summation possible. Furthermore, because the Ward identity is satisfied order by order and because we are able to carry out the infinite order summation and obtain a closed form, renormalization turns out to be very simple and transparent. Here the calculations are performed for a scalar: ?²: φ model, but are easily generalized to other similar models. We also indicate why this rearrangement of the ordinary perturbation expansion is suitable for strong coupling theories, ordinary local field theories as well as dual models.     

Relativistic many-body studies of high density matter

A fully relativistic quantum many-body theory is applied to the study of a model high-density matter which qualitatively describes known nuclear matter. Results pertaining to the equation of state of neutron matter, neutron star mass, vacuum fluctuation corrections, collective modes, exchange energies, and correlation energies are reported.     

Meson exchange corrections and properties of nuclear matter and neutron matter

A calculation of meson exchange corrections to the binding energy as function of the density is presented for nuclear matter and neutron matter. The framework is the application of non-covariant perturbation theory to a field theoretical Hamiltonian. Within a Brueckner-type approximation we restrict ourselves to the calculation of those meson exchange corrections which are due to one meson exchange and which produce no mass renormalization corrections. The results are reported in detail and the structure of the results is revealed. As a net effect, we find that our meson exchange corrections give a repulsion in nuclear matter yielding about 5 MeV less binding at the saturation point. For neutron matter, the effects are very small.     

On the origin of surface states in a correlated local-moment film

The electronic quasiparticle structure of a ferromagnetic local moment film is investigated within the framework of the s-f model. For the special case of a single electron in an otherwise empty energy band being exchange coupled to a fully ordered localised spin system the problem can be solved exactly and, for the spin- electron, some marked correlation effects can be found. We extend our model to incorporate the influence of the surface on the electronic structure. Therefore we modify the hopping integrals in the vicinity of the surface. This leads to the existence of surface states, both for the spin- and the spin- spectral density of states. The interplay between the modification of the hopping integrals and the existence of surface states and correlation effects is discussed in detail. Received: 22 September 1997 / Revised: 12 December 1997 / Accepted: 15 December 1997     

Correcting for incomplete saturation and off-resonance effects in multiple-site saturation-transfer kinetic measurements

The effects of incomplete saturation and off-resonance irradiation on nuclear magnetic resonance saturation-transfer measurements of three-site chemical-exchange rates are discussed. A new method that uses double-saturation measurements is compared with two published methods, one that uses single-saturation measurements and one that uses a single-saturation measurement and a double-saturation measurement. Several formulas are compared for measuring the exchange rate constant k(DE) for exchange from a detected spin D to an exchanging spin E in the presence of exchange from spin D to a competing spin C. For each method, formulas are derived with corrections for incomplete saturation or off-resonance effects, with both corrections, and with neither correction. Exact formulas are available for three exchanging sites with incomplete saturation if there are no off-resonance effects. Off-resonance corrections are imperfect even with complete saturation.     

Curvature effects in the composite model for low-grazing-angle rough-surface scatter

Abstract

The conventional composite surface model used for calculations of radar backscatter treats a large-scale surface component as an ensemble of tilted flat facets. This approach has limitations for low grazing angles. In the paper we develop a new composite model that takes into account the diffraction of an incident field on a curved, large-scale undulating surface. It is shown that, whereas corrections related to curvature effects are small for a steep incidence, those corrections for low-grazing-angle backscatter can be quite essential. Results of numerical simulations of radar backscattering cross sections for two polarizations are presented. Scattering from a surface with one-dimensionally varying roughness is considered. We have studied the role of undulating surface slopes and curvatures in the behaviour of the polarization ratio and found regimes in which the curvature influence on this ratio is more pronounced.     

Electrostatic Surface Waves on Semi-Bounded Quantum Electron-Hole Semiconductor Plasmas

The electrostatic surface waves on semi-bounded quantum electron-hole semiconductor plasmas are studied within the framework of the quantum hydrodynamic model, including the electrons and holes quantum recoil effects,quantum statistical pressures of the plasma species, as well as exchange and correlation effects. The dispersion characteristics of surface electrostatic oscillations are investigated by using the typical values of Ga As, Ga Sb and Ga N semiconductors. Numerical results show the existence of one low-frequency branch due to the mass difference between the electrons and holes in addition to one high-frequency branch due to charge-separation effects.     

Two-photon-exchange and gammaZ-exchange corrections to parity-violating elastic electron-proton scattering

Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and gammaZ-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of gammaZ exchange is in general larger than that of TPE, especially at low momentum transfer Q2相似文献   

Corrections to the strong collision model

The spin dynamics of a diffusing positive muon is investigated and corrections to the strong collision model from quantum-mechanical correlation effects among the nuclear spins are discussed. These effects are treated in the regime of very slow diffusion and their dependence on the applied magnetic field is pointed out.     

On neglecting chemical exchange effects when correcting in vivo (31)P MRS data for partial saturation

Signal acquisition in most MRS experiments requires a correction for partial saturation that is commonly based on a single exponential model for T(1) that ignores effects of chemical exchange. We evaluated the errors in (31)P MRS measurements introduced by this approximation in two-, three-, and four-site chemical exchange models under a range of flip-angles and pulse sequence repetition times (T(R)) that provide near-optimum signal-to-noise ratio (SNR). In two-site exchange, such as the creatine-kinase reaction involving phosphocreatine (PCr) and gamma-ATP in human skeletal and cardiac muscle, errors in saturation factors were determined for the progressive saturation method and the dual-angle method of measuring T(1). The analysis shows that these errors are negligible for the progressive saturation method if the observed T(1) is derived from a three-parameter fit of the data. When T(1) is measured with the dual-angle method, errors in saturation factors are less than 5% for all conceivable values of the chemical exchange rate and flip-angles that deliver useful SNR per unit time over the range T(1)/5 < or = T(R) < or = 2T(1). Errors are also less than 5% for three- and four-site exchange when T(R) > or = T(1)(*)/2, the so-called "intrinsic" T(1)'s of the metabolites. The effect of changing metabolite concentrations and chemical exchange rates on observed T(1)'s and saturation corrections was also examined with a three-site chemical exchange model involving ATP, PCr, and inorganic phosphate in skeletal muscle undergoing up to 95% PCr depletion. Although the observed T(1)'s were dependent on metabolite concentrations, errors in saturation corrections for T(R) = 2 s could be kept within 5% for all exchanging metabolites using a simple interpolation of two dual-angle T(1) measurements performed at the start and end of the experiment. Thus, the single-exponential model appears to be reasonably accurate for correcting (31)P MRS data for partial saturation in the presence of chemical exchange. Even in systems where metabolite concentrations change, accurate saturation corrections are possible without much loss in SNR.     

The effect of the δ(1236) in nuclear matter

The three main corrections to the binding energy of nuclear matter that involve the Δ (1236) are calculated with exchange effects and realistic correlation functions. It is found that their net effect at K_F = 1.36 fm^?1 is small, but that their K_F dependence has a considerable effect on the saturation density.     

Particle size effects on Wulff constructions

The equilibrium structure of small particles is analysed by minimising the total surface energy of atomistic clusters. Large deviations from the bulk Wulff construction are identified for fairly large (~10 nm) particles due to sphere packing corrections. These act as additional edge terms which can be significantly larger than the true edge terms. For a simplified fcc model, it is shown that the fraction of (100) surface drops markedly as the particle size drops because of these packing effects. This can lead to very large particle size effects for a face sensitive catalytic reaction. It is also pointed out that these packing corrections link very small (< 100 atom) cluster to very large particles.     

重夸克偶素质量谱的相对论夸克模型研究（已撤稿）

使用量子场论中准势途径的相对论夸克模型,计算了重夸克偶素的质量谱.所采用的同味正反夸克间的有效相互作用包括通常的直接单胶子交换、单胶子湮没及具有相对论修正的标量和矢量线性禁闭的混合.得到了与实验上肯定的数据符合较好的拟合计算结果，并讨论了湮没项和相对论修正各项对能谱超精细分裂的作用. 关键词： 重夸克偶素 质量谱 相对论修正 湮没势     

Relativistic effects on LEED intensities from Au(111)

Comparison of relativistically and nonrelativistically calculated intensity versus energy profiles in low energy electron diffraction (LEED) from the (111) surface of Au (Z = 79) reveals that relativistic corrections are quite significant. They can however, be obtained in very good approximation by quasirelativistic calculations, in which spin-averaged relativistic phase shifts are used as input for the nonrelativistic multiple scattering formalism. Further, relativistic effects on intensities are found to be comparable to differences arising from different approximations to the exchange part of the ion core potential.     

Diagram Expansions in Nonequilibrium Statistical Mechanics Classical Limit Considerations

A diagram expansion is proposed for calculating traces of the kind Tr{Ae^?itLB} which are of interest for calculating time correlation functions and expectation values in nonequilibrium statistical mechanics. Arbitrary initial conditions are considered. In the classical limit the diagram expansion of FUJITA is obtained. A systematic method for obtaining quantum corrections including exchange and symmetry effects is proposed.     

Single-particle spectrum of a dilute 2D electron gas

Single-particle spectra of a homogeneous 2D electron gas have been calculated in the microscopic functional approach. The effective mass in this system is found to diverge at r _s ? 7. It is shown that the inclusion of the local exchange and correlation corrections to the effective interaction modifies the instability picture from that obtained in the random phase approximation: in the latter, the instability arises away from the Fermi surface, whereas, with the introduction of the corrections, it manifests itself as the divergence of the effective mass.     

The Extraction of Neutron Target Cross Sections from Reactions on Deuterium

The theory of scattering and production reactions on deuterium is developed with a view to the extraction of neutron target amplitudes from analysis of deuterium experiments. Corrections to the spectator model due to the following effects are examined: target particle binding corrections to the Impulse Approximation; (ii) the Pauli principle in charge exchange reactions; (iii) internal or „Fermi”︁ motion of the target particles; (iv) multiple scattering and final state interactions. The closure approximation and the general analysis of single-arm spectrometer experiments are discussed. The connection at high energies and small momentum transfers between the general Watson Theory and the Glauber model is established, and the results of calculations of deuterium corrections for pion and rho photoproduction at high energies are reviewed. “Fresnel” and recoil corrections to Glauber theory are examined. An approximation scheme suitable to the analysis of high energy wide angle coincidence or bubble chamber experiments is developed. A special examination is made of the breakdown of the impulse approximation in the 3-3 resonance region, and of the applicability of lowest order binding and in multiple scattering corrections in this sensitive kinematical region.