New indices for describing the multi-configurational nature of the coupled cluster wave function

New cumulative indices which describe the configurational structure and the degree of 'multiconfigurationality' of the coupled cluster ( CC) wave function have been proposed and tested on some model systems. The indices calculated for the coupled cluster wave functions generated with the CCSD ( single and double excitations) and CCSDT ( single, double, and triple excitations) models were compared with the corresponding values obtained with the full con. guration interaction (FCI) method. The test calculations have concerned cases where the multi-reference character of the wave function increases due to bond stretching.