P. Piecuch et L. Adamowicz, SOLVING THE SINGLE-REFERENCE COUPLED-CLUSTER EQUATIONS INVOLVING HIGHLY EXCITED CLUSTERS IN QUASI-DEGENERATE SITUATIONS, The Journal of chemical physics, 100(8), 1994, pp. 5857-5869
A new procedure for improving the convergence of the reduced linear eq
uation method for solving the single-reference (SR) coupled-cluster (C
C) equations in highly degenerate cases, where the convergence of the
iterative process is often destabilized by ''dangerous'' denominators,
is discussed and implemented. Emphasis is placed on the SR CC methods
involving highly excited clusters, such as the CC method with singles
, doubles, triples, and quadruples (CCSDTQ): The new algorithm is base
d on rearranging and quasilinearizing the nonlinear terms and correcti
ng the energy denominators by the quasilinearized terms. The method is
tested in the SR CCSDTQ calculations for a dissociating single bond.