Externally and internally corrected coupled cluster approaches: an overview

FCIQMC-Tailored Distinguishable Cluster Approach

“… 8 − 19 Generally, these approaches can be divided into two classes of corrections— externally and internally corrected CC methods, and a good overview of these methods can be found in a recent review by Paldus. 20 …”

On the distinguishable cluster approximation for triple excitations

“…[3][4][5] It does not mean, however, that the coupled cluster hierarchy is the most efficient way to approach the FCI limit. On the contrary, results from the distinguishable cluster singles and doubles (DCSD) 6-10 and other methods [11][12][13][14][15][16][17][18][19][20][21][22][23] are usually much better than the coupled cluster singles and doubles (CCSD) results. Additionally, the DCSD equations can be implemented more efficiently than CCSD by employing density fitting or other integral decomposition techniques.…”

Employing broken symmetry effects from unrestricted coupled cluster wave function to determine dynamic and non‐dynamic electron correlation during triple bond breaking in the N2 molecule

“…Thus, in the case of the and cluster contributions, the CCSD(PUCCSD) correlation energy can be calculated using a simple formula based on the standard CCSD theory in which cluster amplitudes and are needed only for this. Higher cluster contributions require additional intermediate calculations to obtain needed the amplitudes t 1 and t 2 that can be obtained by solving the externally corrected CC ( ec CC) equations . More fully, this approach will be discussed in the subsection “Energy effects calculation”.…”

“…Higher cluster contributions require additional intermediate calculations to obtain needed the amplitudes t 1 and t 2 that can be obtained by solving the externally corrected CC (ecCC) equations. [63][64][65][66] More fully, this approach will be discussed in the subsection "Energy effects calculation".…”