Inner-shell Binding Energies Research Articles

Critical appraisal of the semiempirical wavefunctions by calculating ESCA chemical shifts: inner-shell binding energies in halogen atoms

Semiempirical F(1s), Cl(2s), Cl(2p 3 2 ), Br(3d 5 2 ) and I(3d 5 2 ) electron spectroscopy for chemical analysis (ESCA) chemical shifts obtained by using the SCC-MO, AMI and PM3 methods are presented and compared with the experimental data. Agreement with experiment for fluorine and chlorine inner-core binding energy shifts is good, being particularly satisfactory for Cl(2s) electrons. It is concluded that atomic charge distributions in molecules involving highly electronegative fluorine and chlorine atoms are fairly well described by the examined semiempirical approaches. However, Br(3d 5 2 ) and I(3d 5 2 ) ESCA shifts are less successfully reproduced by the semiempirical models. The origins of the corresponding discrepancies are briefly discussed. The use of ESCA shift in the parameterization of semiempirical methods is recommended.

Semiempirical calculations of the ESCA chemical shifts of nitrogen atoms in a chemical environment: failure of the PM3 and AM1 methods

The performance of the AMI and PM3 semiempirical methods in calculating ESCA shifts in the inner-shell binding energies of the nitrogen atom is tested within the electrostatic potential model expressed in the atomic monopole approximation. Relaxation energies accompanying the formation of a positive highly localized inner hole by photoionization are estimated by the equivalent core approach. Both ESCA shifts and relaxation energies are in poor agreement with the experimental data and the available ab initio results. A possible source of errors is detected in the screening ζ constants of the nitrogen atom AOs and its EC counterpart the oxygen atom, which are particularly unsatisfactory in the PM3 approach. A reparameterization of the PM3 and AMI methods for nitrogen is therefore desirable. In contrast to the AMI and PM3 methods, the self-consisted charge method, which is based on the model hamiltonian and retains all overlap integrals, reproduces ESCA shifts and reorganization energies in a satisfactory fashion.

Critical appraisal of some current semiempirical methods in calculating ESCA chemical shifts

Semiempirical MINDO/3 and MNDO methods are tested by calculating N(1 s), O(1 s), F(1 s) and Si(2 p) ESCA chemical shifts. Inner-shell binding energies (ISBE) are estimated by electrostatic potentials exerted at the host nuclei, computed in atomic monopole approximation (AMEP). Reorganization energy upon ionization is taken into account by the equivalent core model whenever possible. The calculated ESCA shifts are in moderately good agreement with experimental data. Comparison with earlier EHT, SCC-MO and CNDO/2 studies shows that the SCC-MO approach is the method of choice if ESCA shifts are to be calculated at the semi-empirical level, as this approach gives a better description of the electron charge distribution in molecules, and in particular gives better estimates of atomic monopoles. It is suggested that ESCA shifts should be used in the empirical adjustment of parameters in semiempirical methods.

Semiempirical calculations of ESCA chemical shifts by the SCC-AMEP model

ESCA chemical shifts give a direct insight into the charge redistribution accompanying formation of chemical bonds. This remarkable feature follows directly from a finding that inner-shell binding energies are closely related to the potentials exerted on the nuclei in question. We have provided extensive evidence which conclusively shows that electrostatic potentials (EP), evaluated in the atomic monopole (AM) approximation, by using the self-consistent charge (SCC-MO) densities, reproduce observed ESCA data in a surprisingly successful way. This approach, abbreviated heretofore the SCC-AMEP model, has also a considerable predictive power. The results have usually an accuracy which is placed in between the chemical and moderate precision. Hence, the salient features of the basic ESCA lines are well described within the AMEP approximation. Finally, the role of the relaxation energy is briefly discussed.

Core-level shifts, isomer shifts and the electron distribution of iron

The radial integrals of 1/ r and 1/ r 3 have been calculated for a number of ion states of Fe. Correlations involving different inner-shell binding energies and atomic charges have been studied and a method for estimating effective valence-electron populations is discussed.

An extension of the fenske-hall LCAO method for approximate calculations of inner-shell binding energies of molecules

The approximate LCAO MO method of Fenske and Hall has been extended to an all-election method allowing the calculation of inner-shell binding energies of molecules and their chemical shifts. Preliminary results are given.

Evaluation of Free-Ion Shifts of Inner-Shell Binding Energies from Ionization Potentials and Electron Affinities

First Page

Dipole moments, atomic charges, and carbon inner-shell binding energies of the fluorinated methanes

Dipole moments, atomic charges, and carbon inner-shell binding energies of the fluorinated methanes

Calculation of K, L, M and N binding energies and K X-rays for elements from Z = 96–120

Atomic parameters should be of great help in identifying the new superheavy nuclei, since X-rays resulting from internal conversion and electron capture are characteristic of the daughter element; and the energies of internal conversion electrons are dependent on the atomic binding energies. Therefore, the inner-shell binding energies and K X-ray energies for the heavy and superheavy elements have been calculated from solutions of relativistic Hartree-Fock-Slater atomic wave functions employing a finite nuclear size. After adding a small semi-empirical correction, we believe that the final results for X-ray energies are accurate to the order of 0.1%.