Unitary-group-based open-shell coupled-cluster method with corrections for connected triexcited clusters. I. Theory

✍ Scribed by Xiangzhu Li; Josef Paldus

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 194 KB
• Volume: 70
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1998)70:1<65::aid-qua4>3.0.co;2-3

✦ Synopsis

Unitary-group-based perturbation theory for both low and high spin open-shell systems is employed to obtain perturbative corrections for the contribution of Ž . the connected triexcited clusters as well as of pseudo-doubles three-body doubles , within the framework of the unitary-group-based coupled-cluster method with interacting w Ž .x singles and doubles UGA-CCSD is . A set of triple excitation operators, generating orthonormal triply excited configurations, which can be employed in both noniterative and iterative coupled᎐cluster calculations involving connected triexcited clusters, is constructed and various schemes for perturbative triple corrections are introduced.