Natural bond orbitals definition

Electronic Diabatic States Definition, Computation, and Applications Localized MO SCF Methods Natural Bond Orbital Methods Natural Orbitals. 

Practitioners of quantum chemistry employed both the visual imagery of nineteenth-century theoretical chemists like Kekule and Crum Brown and the abstract symbolism of twentieth-century mathematical physicists like Dirac and Schrodinger. Pauling s Nature of the Chemical Bond abounded in pictures of hexagons, tetrahedrons, spheres, and dumbbells. Mulliken s 1948 memoir on the theory of molecular orbitals included a list of 120 entries for symbols and words having exact definitions and usages in the new mathematical language of quantum chemistry. 

Theoretically, the radius of an ion extends from the nucleus to the outermost orbital occupied by electrons. The very nature of the angular wave function of an electron, which approaches zero asymptotically with increasing distance from the nucleus, indicates that an atom or ion has no definite size. Electron density maps compiled in X-ray determinations of crystal structures rarely show zero contours along a metal-anion bond. 

Regardless of preference, we are faced with three definitions of the term ionic character, in terms of electronegativity, molecular orbitals, or valence bond wave functions. Any paper on the nature of the H bond must be evaluated in the light of what the writer meant when he wrote that paper. 

We begin the discussion of the nature of the chemical bond with the archetypical example H2. According to the definition of Pauling [6] H2 should be a purely covalently bound species. The partitioning of the energy given in Table 13.1 shows, that this complies with our definition which identifies covalent bonding with orbital interactions. 

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