Theoretical study of the ethylene electronic spectrum and extraction of an r-dependent Hubbard Hamiltonian

The iterative difference-dedicated configuration interaction method has been applied to study the vertical spectrum of ethylene below 9.5 eV. The deviation from experimental estimations is lower than 0.1 eV, including the strongly mixed Rydberg valence 1B1u states. The potential energy curves of the three lowest valence states as a function of the CC bond length are calculated and provide an r-dependent Hubbard Hamiltonian.