The calculation of photoionization cross sections can play a key role in spectral assignments using modeling and simulation. In this work, we provide formal relationships between pole strengths, which are proportional to the section, terms related natural ionization orbital model for ΔSCF calculations. A set numerical calculations developed models is carried out. Pole strength values computed t...

Orbitals, on the one hand, are often considered as auxiliary quantities without physical meaning for various reasons. Slater determinants, e.g., Hartree-Fock or Kohn-Sham determinants, are invariant with respect to unitary transformations of the occupied orbitals. Within densityfunctional theory (DFT) orbitals frequently are considered as quantities that merely generate the electron density but...

We propose and numerically demonstrate that highly correlated electronic wavefunctions such as those of configuration interaction, the cluster expansion, so on, electron wavepackets superposed thereof can be analyzed in terms one-electron functions, which we call energy natural orbitals (ENOs). As name suggests, ENOs are members broad family defined by Löwdin, they eigenfunctions density operat...

We describe an alternative procedure for obtaining approximate Brueckner orbitals in ab initio electronic structure theory. Whereas approximate Brueckner orbitals have traditionally been obtained by mixing the orbitals until the coefficients of singly substituted determinants in the many-electron wave function become zero, we remove singly substituted determinants at the outset and obtain orbit...