A multireference coupled-cluster method using a single-reference formalism.

Persistent Link:
http://hdl.handle.net/10150/185629
Title:
A multireference coupled-cluster method using a single-reference formalism.
Author:
Oliphant, Nevin Horace
Issue Date:
1991
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The coupled-cluster (CC) equations including single, double, triple and quadruple excitations (CCSDTQ) are qraphically derived using Feynman diagrams. These equations are programmed and an iterative reduced linear equation method is used to solve these equations. A few points on the potential curves for the dissociation of some model systems with a single bond (LiH and Li₂) are calculated using CC doubles (CCD), singles and doubles (CCSD), singles, doubles and triples (CCSDT) and CCSDTQ. These calculations demonstrate the magnitude of the CC contributions arising from triple and quadruple excitation amplitudes to the stretching of a chemical bond. A multi-reference coupled-cluster singles and doubles (MRCCSD) method utilizing two reference determinants, which differ by a two electron excitation, is then proposed. One of these determinants is selected as the formal reference determinant. The proposed method is based on the single-reference coupled-cluster equations truncated after quadruples with appropriate restrictions placed on the triple and quadruple amplitudes to allow only those amplitudes which correspond to single and double excitations from the second reference determinant. The computational expense of this method is no more than twice that of singles and doubles from a single reference (CCSD). These equations are programmed and the potential curves for the dissociation of a few model systems with single bonds (LiH, BH, and H₂O) are calculated to demonstrate the correct bond dissociation properties of this method. These calculations also demonstrate how much of the CC energy contribution arising from the triple and quadruple excitation amplitudes can be attributed to single and double excitations from the second reference determinant.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic; Chemistry, Physical and Theoretical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Adamowicz, Ludwik

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleA multireference coupled-cluster method using a single-reference formalism.en_US
dc.creatorOliphant, Nevin Horaceen_US
dc.contributor.authorOliphant, Nevin Horaceen_US
dc.date.issued1991en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe coupled-cluster (CC) equations including single, double, triple and quadruple excitations (CCSDTQ) are qraphically derived using Feynman diagrams. These equations are programmed and an iterative reduced linear equation method is used to solve these equations. A few points on the potential curves for the dissociation of some model systems with a single bond (LiH and Li₂) are calculated using CC doubles (CCD), singles and doubles (CCSD), singles, doubles and triples (CCSDT) and CCSDTQ. These calculations demonstrate the magnitude of the CC contributions arising from triple and quadruple excitation amplitudes to the stretching of a chemical bond. A multi-reference coupled-cluster singles and doubles (MRCCSD) method utilizing two reference determinants, which differ by a two electron excitation, is then proposed. One of these determinants is selected as the formal reference determinant. The proposed method is based on the single-reference coupled-cluster equations truncated after quadruples with appropriate restrictions placed on the triple and quadruple amplitudes to allow only those amplitudes which correspond to single and double excitations from the second reference determinant. The computational expense of this method is no more than twice that of singles and doubles from a single reference (CCSD). These equations are programmed and the potential curves for the dissociation of a few model systems with single bonds (LiH, BH, and H₂O) are calculated to demonstrate the correct bond dissociation properties of this method. These calculations also demonstrate how much of the CC energy contribution arising from the triple and quadruple excitation amplitudes can be attributed to single and double excitations from the second reference determinant.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academicen_US
dc.subjectChemistry, Physical and Theoretical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorAdamowicz, Ludwiken_US
dc.contributor.committeememberArmstrong, Neal R.en_US
dc.contributor.committeememberWigley, David E.en_US
dc.contributor.committeememberSalzman, William R.en_US
dc.contributor.committeememberSmith, Mark A.en_US
dc.identifier.proquest9208028en_US
dc.identifier.oclc711872225en_US
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