On expectation value calculations of one-electron properties using the coupled cluster wave functions

摘要: The ability of various approximate coupled cluster (CC) methods to provide accurate first-order one-electron properties calculated as expectation values is theoretically analysed and computationally examined for BH CO. For actual calculations the infinite number terms value expansion (〈O〉=〈φ¦exp (T+)O exp (T)¦φ〉c) was truncated so that T1T2, T3, (1/2) T2T2 clusters were retained on both sides O. role individual carefully discussed. Inclusion T1, unavoidable, but if triples are essential in energy evaluation, they may play an even more important property expansion, shown case It CC wave function, which exact second order, effectively satisfies Hellmann-Feynman theorem.