Classification of configurations and the determination of interacting and noninteracting spaces in configuration interaction

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Abstract
The n‐particle space of a configuration interaction (CI) calculation, spanned by configuration state functions (CSF's), is partitioned into subspaces defined, relative to a set of zeroth‐order CSF's, by the type of orbital excitation and by the lowest order of the Rayleigh‐Schrödinger perturbative correction contributed by the subspace. A method is given for determining CSF's spanning the ith‐order subspace which contains those and only those functions that have a nonzero interaction through the Hamiltonian with some member of the (i−1)th‐order subspace. These subspaces are anticipated to be of considerable use in structuring and interpreting configuration interaction wavefunctions.