State specific multireference Brillouin-Wigner coupled cluster method with triexcitations

Abstract:
The aim of this project is to formulate and implement the state specific mulltireference Brillouin-Wigner coupled cluster method with triexcitations, in a form suitable for routine applications by an average user of quantum chemical programs. Subsequently we would like to apply the method to systems, which require a very exact treatment of both static and dynamic correlation. Development of an analogous method with mono and bioexcitations has been subject of our research in the past: the method is reliable and allows to treat systems for which the single reference methods fail, however, in order to achieve a quantitative accuracy, it is neccessary to include the effect of triple excitations, at least in an approximate way. We plan to develop the full iterative method with triple excitations as well as less computationally demanding approximations.