Abstract
The properties of Hartree–Fock wavefunctions are used to derive a number of new expressions for upper and lower bounds to the true expectation value of an arbitrary one‐electron operator. These expressions depend on the prior knowledge of upper and lower bounds to the overlap between the Hartree–Fock and true wavefunctions. A new extrapolation method is presented to obtain accurate bounds to these overlaps. A critical study is made of the effectiveness and accuracy of these new error bounds as applied to the systems He, He2, LiH, and Be.