IMPROVED COMPUTATIONAL STRATEGY FOR THE STATE-SELECTIVE COUPLED-CLUSTER THEORY WITH SEMIINTERNAL TRIEXCITED CLUSTERS - POTENTIAL-ENERGY SURFACE OF THE HF MOLECULE
Kb. Ghose et al., IMPROVED COMPUTATIONAL STRATEGY FOR THE STATE-SELECTIVE COUPLED-CLUSTER THEORY WITH SEMIINTERNAL TRIEXCITED CLUSTERS - POTENTIAL-ENERGY SURFACE OF THE HF MOLECULE, The Journal of chemical physics, 103(21), 1995, pp. 9331-9346
The recently developed state-selective (SS) multi-reference coupled-cl
uster (CC) method involving all singly and doubly, and semi-internal t
riply excited clusters from the formal reference configuration [SSCCSD
(T) approach] is tested in the calculation of the potential energy sur
face (PES) of the HF molecule. Both double zeta and double zeta plus p
olarization basis sets are employed and a few different choices of act
ive space are considered. The SSCCSD(T) method provides an accurate de
scription of the entire RES at low cost even for the bond breaking reg
ion, contrary to the results obtained with the perturbative single-ref
erence CCSD(T) method or various limited configuration interaction app
roaches. This is the first application of the new SSCC code, which use
s an improved computational strategy for handling the semi-internal tr
iexcited clusters. Details of this new implementation of the SSCCSD(T)
method are discussed. (C) 1995 American Institute of Physics.