Correlation Effects In States Research Articles

Strong correlation effects in the ionisation of CS 2

The Hell photoelectron spectrum of CS 2 is presented. This spectrum is investigated by two different Green's function calculations. For the outer valence region the origin and assignment of satellite lines of significant intensity is clarified. Strong final state correlation effects are found for the inner valence region showing the so-called breakdown of single-particle picture of ionisation.

Shake-up peak positions and intensities by many-body theory methods

The valence shell X-ray photoelectron spectrum of N 2 is calculated using the equations-of-motion—Green's function method. The inclusion of shake-up basis operator configurations in the primary operator space along with the simple ionization operator configurations allows for the calculation of shake-up peak positions on an equal footing with the simple ionization energies. The important shake-up basis operator configurations are identified using configuration selection techniques similar to those which have been successfully employed in large scale configuration interaction problems, thus minimizing the size of the matrices to be diagonalized. The relative peak intensities are calculated within the plane wave approximation. The intensity equations are analyzed indicating that the relative peak intensities are more sensitive to ground state correlation effects than the peak positions. Modifications of the theory to improve the calculations of shake-up energies are discussed.

I. ATOMIC AND MOLECULAR PHYSICS.ATOMIC EFFECTS IN SOLIDS

This review concerns the origin of the structures of the absorption coefficient measured for solid state samples by several techniques. Because of a close similarity between the solid and gaseous samples spectra, in this energy range (10 to 350 eV), atomic photoionization models are emphasized ; but the most elaborated models introducing correlation effects in both initial and final states are not always sufficient to give a good quantitative agreement with experiment. Some fine structures near the thresholds and a modulation of the spectra fail to be understood in terms of free atom photoionization because of the non-loca!ization of the core hole and the multicenter nature of the field experienced by the photoelectron.

Interpretation of the photoelectron spectrum of N2O4

Many-body Green's function calculations on the ionization spectrum of N2O4 are presented. The ordering of the five ionization potentials below 15 eV is found to be 4ag, 3b2g, 1au(π), 1b1g(π), with increasing binding energy. This ordering differs from that obtained by the application of Koopmans' theorem. Above 15eV binding energy the molecular orbital picture of ionization ceases to be valid. Some of the lines between 15 and 21eV disintegrate because of final state correlation effects. Above 21 eV the intensity associated with each orbital is distributed over numerous lines, leading to a dense line structure extending from about 21 to about 44eV. The energies and spectral intensities of >2300 cationic states have been computed.

Theory of Atomic Structure Including Electron Correlation. I. Three Kinds of Correlation in Ground and Excited Configurations

There are novel correlation effects in excited states and configurations unlike those in closed shells. A theory for general nonclosed shells, and a method for calculation, are developed by separating the correlations into three mathematically and physically distinct types: (1) "internal," (2) "polarization plus semi-internal," and (3) "all-external" correlations. The first two of these are unique to open shells and strongly dependent on number of electrons, symmetry, and $Z$. They are however shown to be calculable by a finite configuration interaction method, and their energy contributions and wave functions are computed using a fully automatic program for 113 states of $1{s}^{2}2{s}^{n}2{p}^{m}(n=0, 1, 2; m=0, 1,\dots{}, 6)$ configurations for $Z=5 \mathrm{through} 11$. Both effects are found to be important in magnitude. The detailed wave functions obtained, which include those of positive and negative ions and of highly excited states containing inner $2s$ holes, are useful for obtaining atomic properties such as transition probabilities. The remaining all-external correlation energy is found to be, as predicted by the present theory, just like the correlation in closed shells, i.e., mainly made up of transferable pair correlations (evaluated in Paper II) and approximately transferable through $Z$ in a given isoelectronic sequence.

Correlation effects in the calculation of ordinary and rotatory intensities

A mixed dipole length-dipole velocity expression for the oscillator strength of an electronic transition is shown to be rather less sensitive to ground state correlation effects than are the ordinary dipole length and dipole velocity formulae. Similar considerations for rotatory strengths show that, in certain, symmetry favoured, cases the results of the dipole length expression are likewise significantly less affected by ground state correlation than are the results of the dipole velocity expression. Some comments are made on the importance of correlation errors in the excited states.