Many-body Brillouin-Wigner second-order perturbation theory: an application to the autoaromatisation of hex-3-ene-1,5-diyne (the Bergman reaction)

The multireference, state specific, second-order, Brillouin-Wigner perturbation theory is applied to the autoaromatisation of hex-3-ene-1,5-diyne, the Bergman reaction. Calculations are reported for the reactant (hex-3-ene-1,5-diyne), the transition state and the product (1,4-didehydrobenzene). A posteriori modifications are made which, in the case of a single reference function, recover the well-known formula of second-order many-body perturbation theory, i.e. Mller-Plesset (MP2) theory, and in the multireference case can be shown to be equivalent to state-specfic multireference Rayleigh-Schrdinger-like perturbation theory. Calculations are performed for a sequence of correlation consistent basis sets and, by extrapolation, complete basis set limits of the energetics of the Bergman reaction are estimated.