Fifth-Order Many-Body Perturbation Theory and Its Relationship to Various Coupled-Cluster Approaches*

摘要: Publisher Summary This chapter presents the fifth-order terms generated by several different coupled-cluster (CC) approaches and compares them with all MBPT diagrams. will enable to analyze steps required compute these terms. Several simplifications are identified. In particular, diagrams arising from T 4 may be obtained only an n 6 algorithm. To enumerate terms, a modified type of diagram is introduced that reduces overall number There methods calculating One most straightforward would collect diagrams, factorize if possible, one one, requiring multiplication two account for their Hermitian conjugates demonstrated comparing, instance, groups Later, results discussed in exhibit calculation energy feasible when carefully implemented applied moderate-sized systems. The must considered substantially reduced taking into fact many have identical values amendable factorization.