Modified Padé approximation scheme to resume the intermediet Hamiltonian QDPT series

Abstract

A modified operator Padé approximation technique is proposed to resume intermediate Hamiltonian perturbation expansions. Due to bilateral projections of the intermediate Hamiltonian onto the space spanned by its main eigenvectors, the influence of impeding matrix elements corresponding to intermediate subspace is avoided. Pilot applications in ab initio QDPT calculations of the ground state of Be atom and potential curves of the ground and excited states of H 2 molecule are reported.