Theory of the chemical bond



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The relation of molecular properties to atomic parameters and to changes in the molecular charge distribution occuring with bond formation is studied quantum mechanically. Implicit Perturbation Theory, a rigorous procedure for obtaining exact wavefunctions from approximate ones, is developed and applied to the dependence of properties of diatomic molecules on internuclear separation. The zeroth-order wavefunction can be selected on the basis of physical realism, mathematical simplicity, availability of previous wavefunctions, or any combination of these, without requiring it to be an eigenfunction of a zeroth-order Hamiltonian. It is never necessary within this formalism to obtain a perturbation operator in explicit form. Perturbed wavefunctions are developed from expansion of the inverse of a matrix whose off diagonal part is small. During bond formation, the interaction between partially charged ions perturbs them; the formalism handles this without a distinguishable electron method. All energy operators are given an equal footing. The dependence of properties on internuclear separation is extracted from expansions of matrix elements of the appropriate operators...