Universität zu Köln

Herrmann, Nils and Hanrath, Michael (2020). Generation of spin-adapted and spin-complete substitution operators for (high spin) open-shell coupled cluster of arbitrary order. J. Chem. Phys., 153 (16). MELVILLE: AMER INST PHYSICS. ISSN 1089-7690

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Abstract

A rigorous generation of spin-adapted (spin-free) substitution operators for high spin (S = S-z) references of an arbitrary substitution order and spin quantum number S is presented. The generated operators lead to linearly independent but non-orthogonal configuration state functions (CSFs) when applied to the reference and span the complete spin space. To incorporate spin completeness, spectating substitutions (e.g., Eivva) are introduced. The presented procedure utilizes Lowdin's projection operator method of spin eigenfunction generation to ensure spin completeness. The generated operators are explicitly checked for (i) their linear independence and (ii) their spin completeness for up to tenfold substitutions and up to a multiplicity of 2S + 1 = 11. A proof of concept implementation utilizing the generated operators in a coupled cluster (CC) calculation was successfully applied to the high spin states of the boron atom. The results show pure spin states and small effects on the correlation energy compared to spin orbital CC. A comparison to spin-adapted but spin-incomplete CC shows a significant spin-incompleteness error.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Herrmann, Nils UNSPECIFIED UNSPECIFIED UNSPECIFIED Hanrath, Michael UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-314129
DOI:	10.1063/5.0026762
Journal or Publication Title:	J. Chem. Phys.
Volume:	153
Number:	16
Date:	2020
Publisher:	AMER INST PHYSICS
Place of Publication:	MELVILLE
ISSN:	1089-7690
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Theoretical Chemistry
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language AUTOMATED IMPLEMENTATION; WAVE-FUNCTION; SINGLET; EXPANSION; EXTENSION; TRIPLET; SYSTEMS Multiple languages Chemistry, Physical; Physics, Atomic, Molecular & Chemical Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/31412