Use Of Configuration Interaction Research Articles

Atomic many-body effects in the 4f XPS of the U5+ and U4+ cations: part II: consequences of orbital relaxation

Ab initio, fully relativistic four component theory was used to determine atomic many-body effects for the 4f X-ray photoelectron spectra (XPS) of U5+ and U4+ cations. Many-body effects were included through the use of configuration interaction (CI) wavefunctions, WF‘s, that allow the mixing of XPS allowed and XPS forbidden configurations. This work extends our earlier study of the U 4f XPS in that the orbitals for the final, ionic states of the cations are allowed to relax in the presence of the 4f core-hole. In the earlier work, orbitals optimized for the initial state were frozen and also used for the final, ionic states. While the main XPS features are similar in both cases, using relaxed orbitals for the ionic states introduces changes in the multiplet splitting and in the 4f5/2 and 4f7/2 spin–orbit splitting. The extent of configuration mixing for the U5+ and U4+ final state WF’s is characterized by the magnitude of the intensity lost by the main peaks to satellites. Overall, the use of relaxed orbitals improves the agreement between the theoretical XPS for the U4+ cation and the experimental measurements for UO2.

Valence Bond Configuration Interaction: A Practical ab Initio Valence Bond Method That Incorporates Dynamic Correlation

A post-VBSCF method, called valence bond configuration interaction (VBCI), is developed here. The method incorporates dynamic correlation, by use of configuration interaction (CI) to improve the energetics after a VBSCF calculation. The levels of CI are fashioned as in the corresponding molecular orbital approach. Thus, VBCIS involves only single excitations, while VBCISD involves also doubles, and so on. The VBCI method retains the simplicity of a VB presentation by expressing the wave function in terms of a minimal number of effective structures that dictate the chemistry of the problem. The method was tested by calculating the bond energies of H2, LiH, HF, HCl, F2, and Cl2 as well as the barriers of identity hydrogen abstraction reactions, X• + X‘H → XH + X‘• (X, X ‘ = CH3, SiH3, GeH3, SnH3, or PbH3). It is shown that VBCIS gives results that are at par with breathing orbital valence bond method. The VBCISD method is better and its results match those of the molecular orbital based coupled cluster CCSD method. Future potential directions of the development of the VBCI approach are outlined.

Calculation of mass polarization for the and states in Li-like ions

Mass polarization arises from a correlation between electronic momenta. In Li-like systems, the effect of core electron correlation dominates. The mass polarization for the and states in B III-Ne VIII is calculated with the use of configuration interaction (CI) wavefunctions. Its dependence on the nuclear charge Z and the atomic states is then studied. The effect of core electron correlation is clearly illustrated with a simple CI wavefunction.

The 2p absorption spectra of 3d transition metal compounds in tetrahedral and octahedral symmetry

The authors present the 2p (L2,3) absorption spectra of first-row transition metal ions in tetrahedral and octahedral crystal field symmetry. These have been calculated using a localized description for the 3dn to 2p53dn+1 excitation including electrostatic and spin-orbit interactions. The spectra are significantly different from those already presented where the 3d spin-orbit interaction was neglected. The spectral shape provides a valence- and symmetry-selective probe. Whereas it changes gradually with the crystal field, abrupt changes in the spectra are indicative of high-spin to low-spin transitions. These spin transitions are accompanied by a strong decrease in the 2p branching ratio. The calculated spectra provide a basis for the use of L2,3 absorption spectroscopy in materials science and biological science. The limitations of these calculations and the use of configuration interaction are discussed.

Electrostatic solvent effect on the circular dichroism of the carbonyl n→π* transition.

The rotatory strength of the n→π* transition in a simple chiral molecule containing a carbonyl group is computed by means of the CNDO/S technique with the use of configuration interaction. A method is proposed to study the modification by a solvent of both position and intensity of the CD spectrum. The calculations allow to separate solvent effects on the electronic distribution and the nuclear geometry. A detailed analysis of the influence of electronic polarization and geometry perturbations induced by the solvent on the CD spectrum is given. In addition, a reversal of the relative stabilities of some conformers in solution is predicted.

Electrostatic solvent effect on the circular dichroism of The carbonyl [formula omitted] transition

The rotatory strength of the n→π ∗ transition ina simple chiral molecule containing a carbonyl group is computed by, means of the CNDO/S technique with the use of configuration interaction. A method is proposed to study the modification by a solvent of both position and intensity of the CD spectrum. The calculations allow to separate solvent effects on the electronic distribution and the nuclear geometry. A detailed analysis of the influence of electronic polarization and geometry perturbations induced by the solvent on the CD spectrum is given. In addition, a reversal of the relative stabilities of some conformers in solution is predicted.

A diatomics-in-molecules case study on the system Be+HF→BeF+H. II. The sensitivity of the potential surfaces to the diatomic input

Potential energy surfaces are presented for a series of diatomics-in-molecules (DIM) models of the reaction Be+HF→BeF+H. This system involves low-lying electronic states of Be and ionic contributions to bonding and is therefore quite complex from the DIM point of view. The various DIM models involve between three and 18 structures and make extensive use of configuration interaction in the diatomic fragments. The potential surface is predicted to have a barrier ∼1.9 eV high for collinear BeFH; at bent configurations this barrier gradually increases. A potential surface having this feature is obtained only if the Be(2s2p) configuration is included in the DIM model. The general problem is raised of how to decide whether a given structure in a DIM model should be retained or not, and of how best to obtain reliable diatomic configuration interaction input data.

Electron correlation, isoelectronic, isonuclear, spin, and excitation aspects of Politzer–Parr partitioning

The effect of electron correlation on the Politzer–Parr procedure for partitioning the electron density of an atom into core and valence regions is investigated by use of configuration interaction (CI) wave functions. Although the effect is generally small, substantial qualitative differences are observed between the 3, 4, and 6 electron cases. Analytical Hartree–Fock (HF) wave functions are used to reveal the trends in isoelectronic and isonuclear sequences. Correlated wave functions, which explicitly include the interelectronic distance, are used to study the effect of spin and electronic excitation on the populations and dimensions of the core and valence regions in the 1sns excited states of He.

The relation between satellite peaks in x-ray emission and x-ray photoemission spectra

A unified model is given to explain the satellite structures observed in x-ray emission spectroscopy (XES) and x-ray photoelectron spectroscopy (XPS) and the relationships between the two. This model accounts for electron correlation by the use of configuration interaction, rather than the heuristic ’’shake-up’’ approach, and actual eigenstates of the system are considered. Two situations are discussed, differing in whether the final XES states have holes in core or valence shells. For core-to-core XES transitions, the correlation-state structure is almost identical in initial and final states. Large satellite intensities may be observed in XPS, but not in XES, in accord with experiment. In core-to-valence XES transitions, the satellite structure should be similar to that observed in XPS, as observed. Detailed CI calculations for the 3s spectra of Ar are compared with measured spectra.

Comparison of calculated oscillator strengths for Si III

Oscillator strengths have been calculated for many of the major transitions in Si III using both dipole length and dipole velocity matrix elements. Three approximations to the many-electron correlation problem are explored and compared: (1) the use of configuration interaction employing a semiempirical frozen core potential; (2) the use of configuration interaction employing a modified Hartree-Fock-Slater basis set; and (3) the use of the Coulomb approximation whereby a wavefunction is constructed with the correct asymptotic behavior. None of these methods as far as they have been carried out here is found to be fully satisfactory. Emphasis is placed upon the difficulty of calculating transition probabilities between high-lying energy levels which are strongly perturbed.

Excited-State Reactivities. III. Use of Configuration Interaction to Calculate Excited-State Localization Energies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcited-State Reactivities. III. Use of Configuration Interaction to Calculate Excited-State Localization EnergiesR. L. Flurry Jr.Cite this: J. Am. Chem. Soc. 1966, 88, 23, 5393–5397Publication Date (Print):December 1, 1966Publication History Published online1 May 2002Published inissue 1 December 1966https://doi.org/10.1021/ja00975a005RIGHTS & PERMISSIONSArticle Views21Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (491 KB) Get e-Alerts Get e-Alerts