Development and application of coupled-cluster methods capable of correctly describing dynamical and non-dynamical correlation in radicals and biradicals

A general scheme for the treatment of multi-reference radical and biradical systems within the coupled-cluster method has been derived, implemented, and applied to a number of problematic systems related to combustion and atmospheric chemistry. These include the vinyl radical, doublet isomers of the HCCO system, and ozone. With respect to traditional coupled cluster techniques, results indicate that the proposed method offers worthwhile accuracy enhancements while concurrently retaining many of the useful convergence properties which allow for the qualitative assessment