Irene Shim

A new interpretation of Hund's first rule

The diagonal elements of the first and second order spinless density matrices have been calculated for the lowest excited1P and3P terms of Be, B+ and C++ using wavefunctions at different levels of approximations published in the literature. The analysis of these functions has resulted in a new interpretation of Hunds first rule in terms of an anisotropic screening effect.

Electronic states and nature of bonding of the molecule NiSi by all electron ab initio HF-CI and CASSCF calculations

All electron ab initio Hartree-Fock (HF), configuration interaction (CI) and multiconfiguration self-consistent field (CASSCF) calculations have been applied to investigate the low-lying electronic states of the NiSi molecule. The ground state of the NiSi molecule is predicted to be1Σ+. The chemical bond in the1Σ+ ground state is a double bond composed of one σ and one π bond. The σ bond is due to a delocalized molecular orbital formed by combining the Ni 4s and the Si 3pσ orbitals. The π bond is a partly delocalized valence bond, originating from the coupling of the 3dπ hole on Ni with the 3pπ electron on Si. Withing the energy range 1 eV 18 electronic states have been identified. The lowest lying electronic states have been characterized as having a hole in either the 3dπ or the 3dδ orbital of Ni, and the respective final states are formed when either of these holes are coupled to the 3pπ valence electron of Si.

Electronic states and nature of bonding of the molecule NiGe by all electron abinitio Hartree–Fock (HF) and configuration interaction (CI) calculations and mass spectrometric equilibrium experiments

All electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations have been applied to investigate the low‐lying electronic states of the NiGe molecule. The ground state of the NiGe molecule is predicted to be 1Σ+. The chemical bond in the 1Σ+ ground state is a double bond composed of one σ and one π bond. The σ bond is due to a delocalized molecular orbital formed by combining the Ni 4s and the Ge 4pσ orbitals. The π bond is a partly delocalized valence bond, originating from the coupling of the 3dπ hole on Ni with the 4pπ electron on Ge. The low‐lying electronic states of the NiGe molecule have all been characterized by the symmetry of the hole in the 3d shell of Ni. The dissociation energy of the NiGe molecule has been determined from our high temperature mass spectrometric equilibrium data in combination with the theoretical results as D○0 =286.8±10.9 kJu2009mol−1. The standard heat of formation of the NiGe molecule has been obtained as ΔH○f,298 =514±12 kJu2009mol−1.

Electronic states of the NiCu molecule determined byab initio Hartree-Fock and configuration interaction methods

The interaction between a Ni atom and a Cu atom in the configurations (3d)9(4s)1 and (3d)10(4s)1, respectively, has been calculated usingab initio Hartree-Fock and configuration interaction methods. The chemical bond between the two atoms is due to a bonding 4sσ molecular orbital. Equilibrium distances, dissociation energies and vibrational frequencies are predicted for the low-lying states. Finally the influence of spin-orbit coupling on the low-lying states is considered.

The nickel-group IV molecules NiC, NiSi, and NiGe

All electron ab initio calculations have been applied to elucidate the electronic states and the nature of the chemical bonds in the molecules NiC, NiSi, and NiGe. The calculations have revealed that the ground states of all three molecules are 1Σ+, but due to the open 3d shell of the Ni atom the molecules have many low-lying electronic states. The NiC molecule is strongly polar, and the low-lying electronic states have been identified as those arising when the angular momenta of the 3Fg Ni+ ion are coupled to the angular momenta of the 4SuC− anion. The chemical bond in the NiC molecule has triple bond character due to the valence bond couplings between the Ni 4s and 3dπ electrons and the C 2p electrons. The chemical bonds in the molecules NiSi and NiGe are very much alike; they are double bonds composed of one σ and one π bond. The σ bond is due to the doubly occupied delocalized molecular orbital composed of the Ni 4s orbital and the Si 3pσ or the Ge 4pσ orbital. The π bond originates from the valence bond coupling between the localized hole in the Ni 3dπ orbital and the valence pπ electron of Si or Ge.