Theoretical Considerations for Idealized pd Systems

Localized and Delocalized Molecular Orbital Description of Covalent Bonds 

The formation of covalent chemical bonds in a molecule is quantum mechanically described by the overlap of atomic orbitals (AO) centered at different atoms 

Determinantal MO s may be obtained by a large number of computational methods based on Roothaan s self-consistent field formalism 94 for solving the Hartree-Fock equation for molecules which differ in degree of sophistication as regards the completeness and kind of the set of starting atomic wave functions, as well as the completeness of the Hamiltonian used 9S . So a chain of various kinds of approximations is available for calculations starting from different ways of non-empirical ab initio calculations 96 , viasemiempiricalmethods for all-valence electrons with inclusion of electronic interaction 95-97 98) 

It has the advantage of allowing a comparison between predictions for a number of structurally related molecular models. If one then carefully checks whether any correlation exists between experimental values and the HMO-mo- 

This radial part is the characteristic unknown for any atom of the periodic system and may be obtained by a variety of computational approaches. It may be determined, for example, numerically by Hartree-Fock calculations or by 

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