研究・研究者
研究会・セミナー
| 演 題 | 「Renormalized and Active-Space Coupled-Cluster Methods: Key Concepts and Recent Advances」 |
|---|---|
| 日 時 | 2012年08月10日(金) 16:00 |
| 講演者 | Prof. Piotr Piecuch （Michigan State Univ.） |
| 場 所 | 分子研 研究棟201号室 |
| 概 要 | The widely used single-reference coupled-cluster (CC) and equation-of- motion (EOM) CC methods, such as CCSD(T) and EOMCCSD, have difficulties with capturing stronger non-dynamic electron correlations characterizing chemical reaction pathways, biradicals, and excited states dominated by two-electron transitions that can often be addressed by exploiting the completely renormalized (CR) and active-space CC and EOMCC approaches. After reviewing the key elements of the method of moments of coupled-cluster (MMCC) equations, on which the CR-CC and CR-EOMCC approaches are based, and the active-space CC and EOMCC theories, illustrated by several molecular applications, we will discuss recent advances in the development and applications of the renormalized and active-space CC/EOMCC methods. Among these advances are the extension of the CR-CC approaches to larger reactive molecular systems with dozens or hundreds of non-hydrogen atoms via the local correlation cluster-in-molecule ansatz and its multi-level extensions, and the promising new possibility of merging the renornalized and active-space CC and EOMCC methodologies into a single mathematical formalism that leads to further, in some cases substantial, improvements in the results for potential energy surfaces along bond breaking coordinates, chemical reaction pathways involving multi-configurational transition states, and singlet-triples gaps in biradical systems. The idea of merging the renormalized and active- space CC/EOMCC methodologies requires a generalization of the moment energy expansions that are behind the CR-CC and CR-EOMCC methods to non-traditional truncations of the cluster and EOM excitation operators, which results in the Flexible MMCC and CC(P;Q) formalisms, and a novel CC(t;3), CC(t,q;3), CC(t,q;3,4), etc. hierarchy. The CC(t;3), CC(t,q;3), CC(t,q;3,4), and other similar approaches correct the energies obtained in the active-space CC or EOMCC calculations, which recover much of the nondynamical and some dynamical electron correlation effects, for the higher-order, mostly dynamical, correlations missing in the active-space CC/EOMCC considerations. We will show that one can obtain a highly accurate description of bond breaking and biradicals, both in terms of the resulting relative and total energies, without turning to sophisticated multi-reference theories or expensive single-reference CC approaches with an iterative treatment of higher-order clusters by combining the active-space CCSDt and CCSDtq approaches with the CC(P;Q)-style corrections due to missing triple or triple and quadruple excitations defining the CC(t;3), CC(t,q;3), and CC(t,q;3,4) approximations. |
| その他 |
講師はミシガン州立大学のPiotr Piecuch教授で、CR-CC, active-space CC, MMCC, CC(P,Q)など様々なCoupled Cluster法の理論開発を行っておられます。 皆様のご参加をお待ちしています。よろしくお願いします。 |
| お問合せ先 | 江原正博 |
