A critical analysis of the "CCSD(T)" model for the study of electron correlation effects in atoms and molecules

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Record Id	29796
Title	A critical analysis of the "CCSD(T)" model for the study of electron correlation effects in atoms and molecules
Contributors	S Wilson
Abstract	A critical analysis of the CCSD(T) ("coupled cluster single and doubles with perturbative triples") method is presented. This method is widely regarded as possibly the best balance between efficiency and accuracy. It includes an a posteriori perturbative correction to the CCSD method for terms associated with triply excited intermediate states which can support 'chemical accuracy' . However, the CCSD method and the augmented theory CCSD(T) fails in the presence of quasidegeneracy. Recent work has shown that multireference methods give more accurate results in studies of systems in which some degree of quasidegeneracy is present. Nevertheless there is continued interest in extending the range of applicability of single reference augmented coupled cluster methods such as CCSD(T). Renormalized CCSD(T) theory , which is based on the method of moments coupled cluster theory, is claimed to be a promising approach which removes the pervasive failing of the standard CCSD(T) method but destroys its "extensivity" property.
Organisation	CCLRC
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Language	English (EN)

Type	Details	URI(s)	Local file(s)	Year
Report	RAL Technical Reports RAL-TR-2003-035. 2003.		raltr-2003035.pdf	2003