Abstract
Multireference Moeller-Plesset perturbation (MRMP) theory with complete active space self-consistent field (CASSCF) reference functions is applied to the study of singlet and triplet valence pi-pi* excited states and Rydberg excited states of benzene in the ultraviolet region. The overall accuracy of MRMP is surprisingly high. The average deviations of the excitation energies from the available experimental values are 0.1 eV for the valence excited states and 0.15 eV for the Rydberg states. A comparison is made with recent results of single reference based methods. It is concluded that MRMP is able to describe excited states with doubly excitation character satisfactory, while single reference based methods are not.