Improved electron propagator methods: An investigation of C4, C−4, and C+4

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Abstract
Several new electron propagator methods for the calculation and interpretation of vertical and adiabatic electron binding energies are applied to C4, C4 −, and C4 +. Among these methods are geometry optimizations of doublet species using neutral and dianionic reference states, renormalized calculations of vertical electron binding energies using unrestricted Hartree–Fock reference states, and analysis of correlated energy differences and corresponding orbitals in terms of one‐electron expectation values. The adiabatic electron affinity of linear C4 is calculated to be 3.69 eV, in excellent agreement with photoelectron spectra. The corresponding result for the cyclic isomer, 2.17 eV, is very close to estimates from Coulomb explosion imaging. Ionization energies for both isomers also are calculated. Geometrical changes accompanying addition or removal of electrons are interpreted in terms of electrostatic interactions between nuclei and electrons assigned to Feynman–Dyson amplitudes.