Electron-propagator calculations on the photoelectron spectrum of ethylene

Electron-propagator calculations are performed on the vertical ionization e nergies of ethylene with a sequence of correlation-consistent basis sets. T wo methods are employed: the nondiagonal, renormalized, second-order (NR2) approximation and the third-order, algebraic, diagrammatic construction. Th e computational efficiency of the NR2 method permits the use of the correla tion-consistent, pentuple zeta basis, which contains 402 contracted Gaussia n functions. As the size of the basis set grows, NR2 results for outer-vale nce ionization energies steadily increase; NR2 errors with the largest basi s set are less than similar to0.15 eV. Agreement with prominent, inner-vale nce peaks is also satisfactory and the ratio of two pole strengths correspo nding to inner-valence, (2)A(g) states is in close agreement with observed intensity ratios. (C) 2001 American Institute of Physics.