Non-orthogonal spin-adaptation and application to coupled cluster up to quadruple excitations
| dc.contributor.advisor | Stanton, John (John F.) | |
| dc.creator | Matthews, Devin Alexander | en |
| dc.date.accessioned | 2014-10-24T15:55:05Z | en |
| dc.date.accessioned | 2018-01-22T22:27:02Z | |
| dc.date.available | 2018-01-22T22:27:02Z | |
| dc.date.issued | 2014-08 | en |
| dc.date.submitted | August 2014 | en |
| dc.date.updated | 2014-10-24T15:55:06Z | en |
| dc.description | text | en |
| dc.description.abstract | The theory of non-orthogonal spin-adaptation for closed-shell molecular systems is presented, with an emphasis on application to the coupled cluster family of electronic structure methods. To aid in the derivation of efficient and compact working equations, a new diagrammatic interpretation of the Goldstone diagrams is derived which only requires a small number of the many distinct diagrams and which directly produces equations in a factored form in terms of “spin-summed” tensor elements. This diagrammatic interpretation is applied to coupled cluster methods with quadruple excitations (CCSDTQ), including coupled cluster with a perturbative correction for quadruple excitations (CCSDT(Q)) and to CCSDTQ gradients and properties. The advantages of the non-orthogonal spin-adaption with respect to simplification and factorization of the working equations and to efficient implementation are presented and discussed. Additionally, specific optimizations of the implementation for often-overlooked issues such as tensor transposition, disk access, and removal of redundant and/or unnecessary operations are detailed. The resulting algorithm is implemented for the CCSDTQ and CCSDT(Q) methods and compared to existing codes, where a one to two order-of-magnitude improvement in efficiency is observed. The new implementation is also used for calculations on several larger molecular systems to illustrate the scalability of the method. | en |
| dc.description.department | Chemistry | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.uri | http://hdl.handle.net/2152/26879 | en |
| dc.language.iso | en | en |
| dc.subject | Coupled cluster | en |
| dc.subject | Electronic structure | en |
| dc.subject | High accuracy | en |
| dc.subject | Spin adaptation | en |
| dc.title | Non-orthogonal spin-adaptation and application to coupled cluster up to quadruple excitations | en |
| dc.type | Thesis | en |