Abstract
A set of intermediate resolvents is formed from the truncated Hamiltonians of Bazley and Fox. On replacing the resolvent operator in Löwdin's bracketing theorem by these intermediate resolvents, one obtains lower‐bound expressions suitable for calculations involving molecules. This method is applied to the ground state of H2+ (exact energy E0 = − 1.10263 a.u. ). The results are −1.15029 a.u. for a one‐term and −1.10438 a.u. for a two‐term truncated Hamiltonian.

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