Relativistic density functional calculations for Pt2

First full-relativistic density functional calculations with the extension of the spin-polarization functional for the relativistic density functional theory in their collinear and noncollinear form are presented here for the molecular system Pt2. The agreement with experiment is very good.     

Relativistic calculations for two- and three-nucleon systems

The relativistic theory for few-nucleon systems developed by Glöckle and Müller is evaluated numerically for a model of scalar particles exchanging scalar mesons to lowest order in the coupling constant. 2-nucleon binding energies and scattering phases and 3-nucleon binding energies are compared with the usual non-relativistic calculation for different choices of the potential. The relativistic treatment gives a weaker binding. The mechanism of this is studied in more detail. We compare our results with the relativistic correction in the 1/c² expansion of Foldy and Krajcik.     

Two-photon photoemission from Ni (1 1 0) and (1 1 1) surfaces

Photoemission was observed when the samples were irradiated with photons in the energy range from 2.5 to 3.3 eV from a tunable dye laser with an intensity of 10⁸Wcm^?2. The emission shows a quadratic intensity dependence. The variation with angle of incidence and polarization is different for the two surfaces. The result obtained from the (1 1 0) surface is discussed with help of the band structure as a two-photon surface photoelectric effect.     

Interpretation of photoemission from Na (1 1 0)

A self-consistent calculation of the electronic structure of the Na (1 1 0) surface, using an embedding method to treat the semi-infinite system, gives a prominent surface resonance peak at 0.75 eV above the Fermi energy. The tail of this resonance extends below E_F at the surface, and it is suggested that surface photoemission from this tail is responsible for the peak in the photocurrent at E_F observed experimentally, A photoemission calculation, with a non-self-consistent surface potential, reproduces the enhancement of the peak as a direct transition moves through it.     

Angle resolved photoemission study of surface states on the Pt(997) vicinal surface

One-dimensional atomic chains can be synthesized on stepped surfaces and the electronic structure of the high vicinal surface plays an essential role in determining the physical properties of atomic chains grown on top of it. We have applied surface analysis techniques to study the surface of a Pt(997) single crystal. The STM image of the surface showed that the surface was uniform with a well defined distance between the terraces. Angle resolved photoemission spectroscopy (ARPES) was used to characterize the electronic states of the Pt(997) surface, and confinement of electrons with wave vector perpendicular to the step direction was observed.     

Relativistic corrections to Coulomb energy calculations

Coulomb energies of nuclei have been calculated using a recently introduced relativistic nuclear shell model¹). The results are very close to those of the usual non-relativistic, isotropic harmonic oscillator shell model, showing the most deviation for heavy elements such as lead.     

Measurements and calculations of photoemission from Ca

The band structure, density of states and photoemission energy distributions for calcium have been calculated from a muffin-tin potential. Photoemission energy distributions have been measured. Transitions between s-p bands are identified. Structure from the empty d-states does not contribute to the primary distribution but is observed in the scattered one.     

Core level photoemission study of Au deposited on Pt(111) in the submonolayer range

A photoemission study, using a synchrotron source, on the deposition of submonolayer amounts of Au on Pt(111) has been performed. The Au 4f emission shifts continuously to higher binding energies for increasing Au coverages. A good fit to the experimental spectra has been obtained by only one Doniac-Sunjic function. We discuss the initial versus final state effects in photoemission experiments on small supported particles.     

Angle resolved photoemission study and calculation of the electronic structure of the Pt(111) surface

Angle resolved photoemission spectra of Pt(111) were measured along the direction of the surface Brillouin zone (SBZ). The electronic structure of a semi-infinite Pt(111) crystal was calculated applying the LMTO-TB approximation to aid interpretation of the spectra. The experimental spectra are well described by the calculated bulk band structure. Both the experiment and calculation reveal a surface state near the Fermi level in the neighborhood of the point of the SBZ.     

Reduction of thin-film ceria on Pt(111) by supported Pd nanoparticles probed with resonant photoemission

Local defects present in CeO_2 ? x films result in a mixture of Ce³⁺ and Ce⁴⁺ oxidation states. Previous studies of the Ce 3d region with XPS have shown that depositing metal nanoparticles on ceria films causes further reduction, with an increase in Ce³⁺ concentration. Here, we compare the use of XPS and resonant photoemission spectroscopy (RESPES) to estimate the concentration of Ce³⁺ and Ce⁴⁺ in CeO_2 ? x films grown on Pt (111), and the variation of this concentration as a function of Pd deposition. Due to the nature of the electronic structure of CeO_2 ? x, resonant peaks are observed for the 4d–4f transitions when the photon energy matches the resonant energy; (hν = 121.0 eV) for Ce³⁺ and (hν = 124.5 eV) for Ce⁴⁺. This results in two discrete resonant photoemission peaks in valence band spectra. The ratio of the difference of these peaks with off-resonance scans gives an indication of the relative contribution of Ce³⁺. Results from RESPES indicate reduction of CeO_2 ? x on deposition of Pd, confirming earlier findings from XPS studies.     

C原子、离子光电离过程的规律研究

基于Dirac-Slater自洽场方法,计算了C原子及各价离子从低能到高能的光电离截面。通过各种理论计算结果的比较,分析了Kramers公式的适用性。定量地考察了多极效应和相对论效应在不同能区对光电离截面的影响,并研究了光电离截面随光子能量、壳层、电离度变化的规律。     

Lifetimes of image-potential states on the Pt(111) surface probed by time-resolved two-photon photoemission spectroscopy

We have investigated the population dynamics of image-potential states on the clean Pt(111) surface. The first two image-potential states have been resolved exhibiting lifetimes of 26±7 fs and 62±7 fs. Those lifetimes are in contrast to the (111) surfaces of Ag and Cu, where the n=2 state is degenerate with bulk states leading to lifetimes shorter than 20 fs. Received: 30 March 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000