title: In search of a rational dressing of intermediate effective Hamiltonians.
abstract: The intermediate effective Hamiltonians are designed to provide M exact energies and the components of the corresponding eigenvectors in the N-dimensional model space, with N > M. The effective Hamiltonian is not entirely defined by these N × M conditions, and several dressings of the Hamiltonian matrix in the model space are possible. Some of them lead to unreliable N - M roots associated with the intermediate model space. This defect appears dramatically when one refers to the weak separability property, namely, the fact that in a noninteracting A···B problem where the model space only involves excitations on A, the consideration of the excitations on B should not affect the spectrum of A. We suggest variants that should maintain the physical meaning of the intermediate roots. Numerical comparisons illustrate the relevance of this proposal.
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, IRSAMC, Université de Toulouse 3 Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France.|Laboratoire de Chimie et Physique Quantiques UMR 5626, CNRS, 118 route de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Barthélémy
authors.initials: B
authors.lastname: Pradines
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, IRSAMC, Université de Toulouse 3 Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France.|Laboratoire de Chimie et Physique Quantiques UMR 5626, CNRS, 118 route de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Suaud
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, IRSAMC, Université de Toulouse 3 Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France.|Laboratoire de Chimie et Physique Quantiques UMR 5626, CNRS, 118 route de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Malrieu