Electron Ab Initio Hartree-Fock Research Articles

Decay of the self-trapped exciton and Frenkel-pair formation in NaF: An ab initio study.

The adiabatic potential-energy surface connecting the triplet self-trapped exciton state to up to the third-nearest-neighbor Frenkel pairs is calculated for ${\mathrm{Na}}_{18}$${\mathrm{F}}_{4}$ clusters using an all electron ab initio Hartree-Fock approach. The correlation effect brings out more details, such as the positions of the nearest-neighbor Frenkel pairs, but does not alter substantially the result of unrestricted Hartree-Fock calculation. No potential barrier larger than 0.2 eV is observed up to the third-nearest-neighbor separation, and it is concluded that the self-trapped excitons can evolve dynamically into stable Frenkel pairs. \textcopyright{} 1996 The American Physical Society.

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 a b i n i t i o 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 kJ mol−1. The standard heat of formation of the NiGe molecule has been obtained as ΔH○f,298 =514±12 kJ mol−1.

Electronic states and nature of bonding of the molecule PdSi by all electron ab initio HF-CI calculations and mass spectrometric equilibrium experiments

Six low-lying electronic states of the PdSi molecule have been investigated by performing all electron ab initio Hartree-Fock (HF) and configuration interaction (CI) calculations. The molecule is predicted to have a3∏ ground state and two low-lying excited states,3Σ− and1Σ+. The electronic structure of the PdSi molecule has been rationalized in a simple molecular orbital diagram. As part of the PdSi molecule the Pd atom essentially retains its (4d)10 ground term configuration. The chemical bond in the PdSi molecule has been interpreted in terms of donation and back-donation of charge. The bond is polar with charge transfer from the Pd to the Si atom. The dissociation energy of the PdSi molecule has been determined from the mass spectrometric equilibrium data in combination with the theoretical results asD 0 o =257±12 kJ mol−1.

A comparative study of the molecules Cu2 and Ag2 by all electron ab initio HF–CI methods

In the present work the molecules Cu2 and Ag2 have been investigated using all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations. The basis sets used were of double zeta quality in general, but the 3d orbital for Cu and the 4d orbital for Ag were represented by triple zeta functions. The wave functions for the Cu2 and the Ag2 molecules have been analyzed in detail. Calculated spectroscopic constants have been derived and compared to experimental data, where available. Both for the Cu2 and the Ag2 molecules the calculated spectroscopic data vary considerably as the CI calculations exclude or include excitations from the valence d orbitals. The chemical bonds for both molecules are single bonds almost entirely due to sσg molecular orbitals.

The generalized valence bond π orbitals of ethylene and allyl cation

Using a fixed sigma core obtained from full electron ab initio Hartree-Fock calculations, the spatially projected GVB orbitals for the pi electron systems of ethylene and allyl cation are reported. The GVB(SP) method generates wavefunctions possessing the correct spatial and spin symmetry without restricting the nature of the individual orbitals. The GVB(SP) wavefunction provides a simple interpretation of the molecule in terms of orbitals each containing a single electron. The resulting total energies and excitation energies agree very well with full configuration interaction calculations.