Core electron binding energies in heavy atoms

Inner shell binding of electrons in heavy atoms is studied through the relativistic density functional theory in which many electron interactions are treated in a local density approximation. By using this theory and the Δscf procedure binding energies of several core electrons of mercury atom are calculated in the frozen and relaxed configurations. The results are compared with those carried out by the non-local Dirac-Fock Scheme.K-shell binding energies of several closed shell atoms are calculated by using the Kohn-Sham and the relativistic exchange potentials. The results are discussed and the discrepancies in our local density results, when compared with experimental values, may be attributed to the non-locality and to the many-body effects.     

核衰变产生的X射线和俄歇电子数据计算

核衰变过程中,内转换电子发射和电子俘获能在原子电子壳层内留下空穴.其他原子电子壳层的电子将填补这些空穴,其原子电子位置将重排,并发射X射线和俄歇电子.X射线和俄歇电子的能量由原子电子结合能计算得到,X射线和俄歇电子的强度分别由内转换电子发射和电子俘获在原子电子壳层内留下的空穴数,X射线荧光产额,和空穴转移系数计算得到.本文简要介绍核衰变产生的X射线和俄歇电子数据的计算方法、计算程序与工作流程,并以核衰变为例说明其具体应用和简要讨论与总结.     

An ESCA study of the molecular core binding energies of the fluorobenzenes

The molecular core binding energies of the complete series of the fluorobenzenes have been measured using ESCA. The experimental values are interpreted in terms of all valence electron CNDO/2 SCF MO calculations. The measured binding energies have been used, in conjunction with previous data, to calculate charge distributions. Some comment is made on linewidths and charging effects.     

Electron binding energies in the study of adsorption by photoelectron spectroscopy: The reference level problem

There has been much discussion in the literature concerning the definition of a suitable reference level for electron binding energies in solids and adsorbed species. The reference level in molecular photoelectron spectroscopy is the vacuum level at infinity; and, in order to calculate the total energy of the system, it is also the appropriate reference level for electron binding energies in solids. We show that for solids and adsorbates the vacuum level is not a chemically useful reference level. This is because the absolute binding energy is affected by electrostatic potentials which are unrelated to the local chemical bonding. It is concluded that there is no experimental energy level, to which adsorbate binding energies can be referenced, which allows one to make an absolute measurement of binding energy shifts due to surface interaction. Approaches to obtaining chemically meaningful binding energies from the photoelectron spectra of adsorbates are discussed.     

A CNDO/2 study of σ- and π- relaxation energies and core electron binding energy shifts in some simple molecules

A relaxation potential model has been used to study relaxation energies and shifts in core electron binding energies for some substituted alkenes and carbonyl compounds in terms of σ- and π-contributions.The conclusions from this study may be summarized as follows:(A) For the series R₁R₂C^*CH₂ and R₁R₂C^*O: (i) The total shifts vary in a regular manner, similar to the shifts in saturated systems; (ii) The variation in σ-relaxation energies is greater than the variation in π-relaxation energies.(B) For the series R₁R₂CCH₂ and R₁R₂CO: (i) There is little variation in the σ-relaxation energies; (ii) The π-relaxation energies show moderately large variations and the higher values are associated with unsaturated substituents which can donate π-electrons to the core-ionized atom via the conjugated π-system; (iii) The π-relaxation energies in the fluorinated systems are similar to those in the unsubstituted molecules; and (iv) The large -ve π-shift in the fluorinated systems results from a ground state build up of electron density at the site of core ionization.     

DFT calculation of core– and valence–shell electron excitation and ionization energies of 2,1,3-benzothiadiazole C6H4SN2, 1,3,2,4-benzodithiadiazine C6H4S2N2, and 1,3,5,2,4-benzotrithiadiazepine C6H4S3N2

The vertical core– and valence–shell electron excitation and ionization energies of the three title molecules, 1–3, were calculated by density functional theory (DFT) using adequate functional for each type of processes and atoms under study. The inner shells treated were C1s, N1s, S1s, S2s, S2p. Molecular geometry was optimized by DFT B3LYP/6-311 + (d,p). The basis set of triple zeta plus polarization (TZP) Slater-type orbitals was employed for DFT calculations. The ΔSCF method was used to calculate ionization energies. The average absolute deviation (AAD) from experiment of 26 valence-electron ionization energies calculated by DFT for the three molecules 1–3 was 0.14 eV; while that of 24 calculated core-electron binding energies (CEBEs) from experiment was 0.4 eV. Selected core excitation energies were calculated by the multiplet approximation for the three molecules. The AAD of twelve calculated core excitation energies by the multiplet approximation that exclude S2s cases was 0.56 eV. Time-dependent DFT (TDDFT) was employed to calculate the excitation energies and corresponding oscillator strengths of core- and valence-electrons of the molecules. Some selected occupied core orbitals were used to calculate the core-excitation energies with the TDDFT (Sterner–Frozoni–Simone scheme). The core excitation energies thus calculated were in an average error of ca. 28 eV compared to observed values. They were shifted to the value calculated by the multiplet approximation. Convoluted spectra based upon the shifted energies and accompanying oscillator strengths reproduce low-energy region of observed spectra reasonably well, whereas they deviate from experiment in high-energy region. Reasonable agreement between theory and experiment was obtained for the valence electron excitations of the molecules.     

Influence of elastic scattering on the measurement of core-level binding energy dispersion in X-ray photoemission spectroscopy

We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to the determination of core level binding energies in Au(111) and Cu₃Au(100). We find that an artificial shift is created in the binding energies of the Au 4f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core level emission itself. Using a simple model, we are able to reproduce the angular dependence of the shift and relate it to the anisotropy in the electron emission from the bulk layers. Our results demonstrate that interpretation of variation of the binding energy of core-levels should be conducted with great care and must take into account the possible influence of artificial shifts induced by elastic scattering.     

内转换电子能量及绝对强度计算

简要介绍γ跃迁的内转换电子能量及绝对强度的计算方法,并以实例说明其具体应用.     

低能电子入射电离He原子二重微分截面的理论研究

研究了低能电子入射单电离He原子的二重微分截面(DDCS)，通过对散射电子三重微分截面在全空间的角度积分得到敲出电子的DDCS.分别用DS3C模型和BBK模型计算了入射能为26.3，28.3，30.3，32.5，34.3，36.5和40.7eV时，低能电子入射电离He原子的DDCS；研究表明：DS3C的计算结果，除在低入射能(比如26.3eV)和小敲出角之外，均能与绝对测量的实验结果较好地符合.此外，对直接和交换效应也进行了研究，给出了交换效应对截面的贡献.     

Impact of shell thickness on exciton and biexciton binding energies of a ZnSe/ZnS core–shell quantum dot

Impact of shell structure on the exciton and biexciton binding energies has been studied in a ZnSe/ZnS core–shell quantum dot using Wentzel–Kramers–Brillouin (WKB) approximation. For excitons, the binding is caused by the Coulombic as well as the confinement potentials while biexciton binding energy is determined by taking into account the exchange and correlation effects. The exciton binding energy was found to increase initially with increasing shell thickness which reaches saturation at larger shell thickness. On the other hand, the biexciton binding energy exhibits a crossover from the bonding to antibonding state with increasing shell thickness for smaller core radius of the quantum dot.     

Experimental core-hole ground state energies for the elements 41Nb to 52Te

Photoelectron spectra from metallic systems always show asymmetric core lines. One effect of this asymmetry is to shift the peak position of a core level spectrum away from the ground state energy of the core hole state. In this letter, M and N core level binding energies for the 5th period elements are reported which have been corrected for the effect of the asymmetry. In some cases the relative energy positions have been compared to accurate X-ray data. The results indicate that even when fairly broad core electron lines are involved, accurate core level separations can be determined.     

Energy calibration in electron spectroscopy and the re-determination of some reference electron binding energies

Measured binding energies were found to vary with the choice of reference binding energies used in instrument calibration. Inadequate linearity of the spectrometer energy scale was eliminated as a source of the error. Primary calibration methods were considered, and tried. The instrument was finally set up by the two X-ray wavelength method, using Al Kα and the Ag Lα,β radiations. Subsequent re-determination of electron binding energies for noble metals and copper showed differences from previously adopted values that would be important in calibration work.     

Direct experimental determination of the dispersion of a final state energy band

We report the first absolute and continous experimental determination of the dispersion of an unoccupied electron energy band in copper. This has been achieved by monitoring the extremal behaviour of binding energies in angular resolved photoelectron energy distribution curves obtained with a tunable light source. By this method the absolute value of the wave vector for transitions originating from the symmetry line ∑ was determined. The experiments confirm that the final state band deviates strongly from a parabola.     

One-electron spectrum of Yb+: Relativistic energies,transition probabilities and dipole polarizability

Calculations are reported of relativistic ionization energies and transition probabilities in the one-electron spectrum of singly-ionized ytterbium. The relativistic model potential approach used takes into account both valence-core electron exchange and correlation. The influence of polarization of the core by valence electrons on ionization energies and transition probabilities has been studied. Strong cancellation effects have been found for higher transitions of the principal series; these affect both transition probabilities and relative line strengths. The energies are predicted for some states which have not yet been experimentally localized. The static dipole polarizability for Yb⁺ is estimated to be 48.18 g₀³ from computed oscillator strengths; this estimate is compared with lower bounds determined from experimental data.     

Dynamic correlation

From a knowledge of the Hartree-Fock and exact non-relativistic energies of atoms, the correlation energy E_c, as defined by Lowdin, may be calculated. For atoms this correlation is defined as dynamic correlation. The separate like-spin and unlike-spin contributions, E_cσσ, E_cαβ, may be calculated as a sum of pair energies from quantum chemistry; we have used the unrestricted M?ller-Plesset second-order algorithm, and then scaled them to give E_c. These three values may also be computed using dynamic correlation functionals, with the Stoll partitioning. The VWN, LYP and P91 functionals were studied for the atoms from H to Ar. Although the total correlation energies of LYP and P91 are similar, only P91 gives a semi-sensible breakdown into the E_cσσ, and E_cαβ components. It is immediately apparent that a new functional, OPTC, derived from the P91 components as 0.6625 x E_cσσ, + 1. 1015 x E_cαβ is an improvement (its mean absolute error is only 0.006 E_h). Using the recently introduced improved exchange functional OPTX (obtained through a fit to the HF energies of atoms), Kohn-Sham calculations were performed on the atoms using the OPT(=OPTX + OPTC) functional. The total energies have a mean absolute error of 0.006 E_h. The study then moves to molecules. First it is shown that the dynamic correlation energy contribution to the dissociation energies is very similar (within 2kcalmol^?1 in most cases), whether it is calculated with LYP, P91 or OPTC. A calculation is then made of the HF contribution, the dynamic contribution through OPTC and the left-right contribution through OPTX, to molecular binding. In many cases the sum agrees with the observed value, but in some cases the prediction is significantly in error, e.g. O₂ is overbound by 10 kcal mol^?1. Thus either OPTX or OPTC or both are inadequate. An attempt was made to determine improved local exchange and correlation functionals by fitting to both atomic and molecular data, but this was unsuccessful. The conclusion is that the method is close to the limit of accuracy achievable from separately optimized local exchange and correlation functionals. Finally, a new hybrid functional O3LYP, which is a substantial improvement on B3LYP, is presented.     

Simultaneous Effects of HydrostaticPressure and Conduction Band Non-parabolicity on BindingEnergies and Diamagnetic Susceptibility of a Hydrogenic Impurityin Spherical Quantum Dots

Simultaneous effects of conduction band non-parabolicity and hydrostatic pressure on the binding energies of 1S, 2S, and 2P states along with diamagnetic susceptibility of an on-center hydrogenic impurity confined in typical GaAs/Al_xGa_1-xAs spherical quantum dots are theoretically investigated using the matrix diagonalization method. In this regard, the effect of band non-parabolicity has been performed using the Luttinger-Kohn effective mass equation. The binding energies and the diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot radius and different values of the pressure in the presence of conduction band non-parabolicity effect. The results we arrived at are as follows: the incorporation of the band edge non-parabolicity increases the binding energies and decreases the absolute value of the diamagnetic susceptibility for a given pressure and radius; the binding energies increase and the magnitude of the diamagnetic susceptibility reduces with increasing pressure.     

Adsorption of H2 and CO on clean and oxidized (110) Pt

Binding states and sticking coefficients of CO and H₂ on clean and oxide covered (110) planes of Pt are examined using flash desorption mass spectrometry to characterize binding states and Auger electron spectroscopy (AES) to characterize oxide densities. It is found that on the oxide both adsorbates have new binding states with significantly higher binding energies than on the clean surface. For H₂ the binding states associated with the clean surface are also shifted to higher energies as the oxide coverage increases. The oxide state for H₂ desorbs with first order kinetics, and isotope exchange experiments are used to examine exchange between isotopes and between states. The initial sticking coefficients for CO are 1.0 and 0.85 on clean and oxidized surfaces, and the initial sticking coefficient for H₂ increases from 0.15 on the clean surface to 0.28 on the oxidized surface. Enhanced bonding on the oxide is interpreted in terms of models involving microfacets, electronic structure alteration, and compound formation.     

Electronic interaction between valence and dipole-bound states of the cyanoacetylene anion

The electron attachment properties of cyanoacetylene HCCCN are investigated with particular emphasis on the coupling between dipole-bound and valence states. As an initial step both the dipole-bound and the valence state of HCCCN^- are studied separately using high level ab initio methods. Predictions for the geometry of the valence anion, the electron binding energy of the dipole-bound state, the energy of the temporary anion associated with vertical attachment into the valence state, the vertical detachment energy of the valence anion, and the adiabatic electron affinity of HCCCN are given. Our results indicate that the electron affinity found in the NIST web-book is not that of HCCCN but of some other C₃HN species. The two anionic states interact with each other, and we study their electronic coupling by computing the two electron binding energies along one- and two-dimensional cuts through the potential energy surfaces, and fitting a diabatic model potential to the ab initio data. In particular, the two-dimensional cuts allow us to examine the geometry dependence of the electronic coupling, and to ask the question whether the coupling elements inferred from one-dimensional cuts represent typical values. Moreover, the influence of the theoretical method on the computed coupling elements is investigated, and the possibility of employing the diabatic model potential as a mean to extrapolate bound state binding energies into the metastable domain is pointed out.