Theory of the chemical bond

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...