P-EOM-MBPT

The partitioned equation-of-motion second-order many-body perturbation theory [P-EOM-MBPT(2)] [67] is an approximation to equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) [17], which will be fully described in Section 2.4. The EOM-CCSD method diagonalizes the coupled-cluster effective Hamiltonian H = [HeTl+T2) in the singles and doubles space, i.e.,... 

It may be noticed that by virtue of being a dressed Hamiltonian including the effect of correlation, diagrams 37-39 account for some of the CIS(D)-type correlation corrections (22-24) to CIS (diagrams 35 and 36). There is no need to make ad hoc adjustments to diagrams to ensure size correctness because diagram 37 (unlinked) cancels exactly between the ground and excited states. In other words, P-EOM-MBPT(2) has the factorization approximation built in. 

EOM-CC method (p. 548) deexcitations (p. 550) many body perturbation theory (MBPT) (p.551)... 

P —2co co,co) calculations on ammonia, and used them to scale static MBPT(2), CCSD, and CCSD(T) values. They also calculated EOM-CC fi(—co co, 0) directly. They obtained EOM-CC P —2co CO, (o) by using the dispersion relations and scaling the static CCSD(T) P(—2co co, co). Rice and Handy performed TDCHF and MP(2) calculations for fi(—co co,0) and P —2co co, co). There have also been MCSCF QRF calculations of P —2(0-, CO, co), and there is an experimental value. These results are compared in Tables 2 and 3. It is clear that there is a long way to go before these calculations can be said to be converged. 

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