# MULTICONFIGURATION WAVEFUNCTIONS FOR THE $\Pi$-ELECTRON STATES OF ETHYLENE

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 Title: MULTICONFIGURATION WAVEFUNCTIONS FOR THE $\Pi$-ELECTRON STATES OF ETHYLENE Creators: Bender, Charles F.; Dunning, T. H., Jr.; Goddard, W. A., III; Hunt, W. J.; Noyes, Arthur A.; Schaefer, H. F., III Issue Date: 1972 Publisher: Ohio State University Abstract: Ab initio calculations have been carried out on the $N(\Pi^{2})$, $T(\Pi \Pi^{*})$ and $V(\Pi \Pi^{*})$ states of ethylene in a planar nuclear configuration. A double zeta’’ gaussian basis, augmented by diffuse functions, was used. A wide variety of configuration interaction wavefunctions (including as many as 1605 configurations), optimized by the iterative natural orbital method, were computed. The calculations predict vertical excitation energies of $\sim 4.2$ eV for the $T(\Pi \Pi^{*})$ state and $\sim 8.1$ eV for the $V(\Pi \Pi^{*})$ state. The spatial extent of the ground and excited triplet states is that of a normal valence state with $\langle x^{2} \rangle \sim 12$ $bohr^{2}$. The excited singlet state, on the other hand, is found to be quite diffuse or Rydberg-like, $\langle x^{2} \rangle \sim 35 bohr^{2}$; electron correlation decreases $\langle x^{2} \rangle$ by 30\% from the Hartree-Fock value (52 $bohr^{2}$). Description: Author Institution: Lawrence Livermore Laboratory; Laboratory of Chemical Physics, California Institute of Technology; Department of Chemistry, University of California Berkley URI: http://hdl.handle.net/1811/9189 Other Identifiers: 1972-Y-3