Convergence of the Rayleigh-Schrödinger perturbation expansions for the energy levels of the Pariser-Parr-Pople model of the benzene molecule

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Abstract
Estimates of the radii of convergence of the Rayleigh‐Schrödinger perturbation expansions for various energy levels of the π‐electronic model of the benzene molecule, described by the PPP (Pariser‐Parr‐Pople) Hamiltonian, in both weakly and strongly correlated limits, were determined using a ``generalized'' Cauchy criterion and the numerically determined coefficients of the pertinent expansions. The difficulties associated with the numerical approach to the problem, in which one is always limited to a finite number of terms in the expansion, are discussed and the appropriate procedures enabling us to overcome, at least partially, these problems are outlined.