Abstract
The multireference Moeller-Plesset (MRMP) method is a feasible and accurate way to take into account the electronic correlation. The static electronic correlation is involved in reference complete active space self-consistent field wavefunctions, while the dynamic correlation is treated in the second order perturbation method. So far various applications have been made for excitation spectra and MRMP has proved to be a powerful tool for excited states as well as for the ground state of molecules. In this review, some applications to the excitation spectra of alternant hydrocarbons and some other organic molecules and to an accurate estimation of the ground state potential surface are presented: polyacene(benzene, naphthalene), linear polyenes, five-membered ring compounds (cyclopentadiene, pyrrole, and furan), and unimolecular decomposition of formaldehyde. Furthermore, two topics are also discussed as to the interpretation of the electronic structures: pairing properties of alternant hydocarbon and a complete active space valence bond (CASVB) description of the electronic states.