Open-shell Nature Research Articles

Correlation Energy of Atomic Nitrogen

The Brueckner-Goldstone many-body perturbation theory is applied to study the electronic structure of the atomic nitrogen in its ground $^{4}S$ state. A complete orthonormal set of the ${V}^{N\ensuremath{-}1}$ single-particle states with angular symmetry up to $l=5$ is explicitly used to calculate the correlation-energy diagrams. The contribution from higher $l(>5)$ is estimated by a hydrogenic approximation of the continuum wave functions. Our final correlation energy is -0.1895 \ifmmode\pm\else\textpm\fi{} 0.003 a.u., as compared with -0.1886 \ifmmode\pm\else\textpm\fi{} 0.0094 a.u. from the semiempirical estimate made by Veillard and Clementi. The sum of the exchange-core-polarization and pair-correlation-energy diagrams give a total of -0.207 28 a.u., which is 110% of the semiempirical estimate. This contains a contribution of -0.006 10 a.u. (3.2%) from $l>3$ states and -0.058 25 a.u. (31%) from the excitations into the valence $2p$ orbitals, the latter arising from the open-shell nature of the nitrogen atom. The overestimate (10%) of the correlation energy is remedied by the pair-pair correlation of 0.011 37 a.u. (6%) and the many-electron (three and four) effect of 0.006 42 a.u. (3.4%). A comparison with earlier configuration-interaction results is also made.

Photoelectron spectra of transition-metal hexafluoroacetylacetonates and the supposed breakdown of Koopmans' theorem in these compounds

The initial parts of the photoelectron spectra of the trishexafluoroacetylacetone complexes of chromium, iron, and cobalt are presented; from the spectra there is no evidence for any inversion of orbital sequence upon ionization, but the chromium and iron complexes show an effect which may be ascribed to their open-shell nature.