John W. D. Connolly

On some approximations in applications of Xα theory

An approximate Xα functional is proposed from which the charge density fitting equations follow variationally. LCAO Xα calculations on atomic nickel and diatomic hydrogen show the method independent of the fitting (auxiliary) bases to within 0.02 eV. Variational properties associated with both orbital and auxiliary basis set incompleteness are used to approach within 0.2 eV the Xα total energy limit for the nitrogen molecule.

On first‐row diatomic molecules and local density models

The total Xα energy accurate to 0.3 eV is computed for H2, B2, C2, N2, O2, CO, and F2. Relative to experiment, the Xα model (α=0.7) is accurate to within ΔRe=0.1 bohr, ΔDe=2 eV, and Δωe=300 cm−1 for these molecules. Except for the lightest first‐row diatomic molecules, the Xα and experimental dissociation energies are bracketed by those of the Hartree–Fock model (from below) and the Local Spin Density model (from above).

Total Energy in the Multiple Scattering Formalism: Application to the Water Molecule

A scheme for obtaining the statistical total energy in the multiple scattering formalism is presented. Calculations are then carried out on the water molecule, which has been thoroughly investigated by ab initio LCAO MO SCF and experimental methods, in order to test the reliability of the method. The one‐electron energies, ionization potentials, and vibrational potential curves are reported. Some advantages and limitations of the method are discussed in light of these results.

Calculation of molecular ESCA spectra by the multiple‐scattering‐Xα method

The recently developed multiple‐scattering method has been applied to the solution of the approximate SCF (Xα) equations. Through the concept of the transition state, it is possible with this method to estimate the ionization energies measured in electron spectroscopy (ESCA) experiments. Comparisons with experimental ionization energies for several small molecules (i.e., CF4, NH3, N2, CO, NO, CO2, N2O, C3O2) show in general, better agreement than semiempirical orbital energies and about the same as ab initio MO‐LCAO‐SCF orbital energies.

Tight binding molecular dynamics study of Ni clusters

A minimal parameter tight binding molecular dynamics scheme is used to study Nin clusters with n≤55. We present theoretical results for relaxed configurations of different symmetries, binding energies, and normal vibrational frequencies for these clusters. Our results are in good agreement with experiment and previous theoretical predictions. We also compare relative stabilities of fcc structures with icosahedral structures. In particular, we find that for clusters whose size allows them to form a close icosahedral geometry (normal or twinned), the closed icosahedral structures yield larger binding energies than fcc structures. The fcc structures, in turn, are found to be more stable than open icosahedral structures for n≤55. Additionally, results for normal vibrational frequencies and ionization energies for n≤10 are also presented. The present results, along with previous successful applications of the method on semiconductor systems, indicate that tight‐binding molecular dynamics scheme can be relied o...

Calculation of the ionization energies of the sulphur hexafluoride molecule by the multiple scattering method

Abstract The multiple-scattering (or scattered-wave) model has been applied to the sulphur hexafluoride molecule, using an approximate Hartree-Fock potential of the X α type. The calculated ionization energies are compared with the data from the X-ray photoelectron spectroscopy (ESCA) experiments, and found to be in better agreement than either the ab initio (SCF MO LCAO) or semi-empirical (CNDO) results.

Spin and bonding properties and optical spectra of octahedral transition metal complexes using the multiple scattering Xα method

Spin-polarized multiple scattering calculations using scaled local exchange are performed for the following octahedral clusters: TiF63−, CrF63−, CrCl63−, MnF62−, MnF64−, FeF63−, NiF62−, NiF64−, and NiCl64−. Good agreement is obtained with EPR and NMR measurements of transferred hyperfine interactions. fσ is found to be larger than fπ even for the d3 systems. For the optical spectrum the method predicts the shift quite well when Cl is substituted for F.

Optical spectra of some octahedral transition metal fluorides as calculated by multiple scattering method

Abstract The electronic spectra of the octahedral clusters TiF 3− 6 , CrF 3− 6 , MnF 2− 6 , NiF 2− 6 , and NiF 4− 6 are calculated using the multiple-scattering model with statistical exchange. The agreement is satisfactory, indicating that this simple method can be used for detailed investigations of the electronic structure of transition metal complexes.

MS-Xα calculations on boron trihalides and comparison with their photoelectron spectra☆

Abstract The multiple-scattering Xα model has been applied to the sequence of boron trihalides BX 3 where X = F.C1. Br, and I. Transition state calculations show good agreement with the experimental ionization potentials measured by photoelectron spectra.

Ms-Zα calculation of the energy-level structure of XeF6

Abstract The ionization and total statistical energies of XeF 6 are calculated at the experimental bond distance, along with the statistical energy and ionicities for the separated ions, using the multiple-scattering-Xα model. The ionization energies are in better agreement with experiment than ab initio results.