Complex coordinate calculation on an ethylene shape resonance

This paper reports results of calculations of the energy and width of a 2B/sub 2g/ shape resonance in the ethylene molecule. A second-order treatment utilizing the coordinate-rotated electron propagator yields results in good agreement with experiment. Variation in basis set composition is shown to lead to varying estimates of the computed energy and width; the latter is found to be especially sensitive to basis composition. Fourier transforms of the Dyson orbital on resonance produce the expected quasiparticle momentum distribution, with numerically computed energy and width consistent with the coordinate rotation calculation. Off resonance, this momentum distribution is multimodal, and therefore not representative of a localized state