Multireference Theory based on COLUMBUS 

Goals and Approaches

Available methods include multiconfiguration selfconsistent field (MCSCF), multireference configuration interaction (MRCI)  and MR-averaged quadratic coupled cluster (MR-AQCC) methods. For more details see COLUMBUS – A Program System for Advanced Multireference Theory Calculations.

Primary COLUMBUS collaboration partners: Thomas Müller (Jülich Supercomputing Centre, Jülich, Germany), Felix Plasser (University of Vienna, Vienna, Austria) and Ron Shepard (Argonne National Laboratory, Argonne, Ill., USA)

Recent development: Local electron correlation treatment based on the weak pair approach:

The removal of simultaneous single excitations out of the weak pairs (see picture to the right) is based on the reference doubly occupied space only, leading to a straightforward program implementation and a conceptual simplicity in terms of well-defined localized orbitals. Reductions of up to an order of magnitude in the configuration space expansion and in computer time for the Davidson diagonalization step are found.

More details: J. Chem. Theory Comp., in press