Coupled Cluster (CC) Theory is the most accurate many-body ab-initio Quantum Mechanical Theory for predicting molecular energetics and spectra. Although many variants of CC have been developed, all of these methods have their own pros and cons in terms of computational efficiency and structural simplicity and thus their general usability. The single reference coupled cluster (SRCC) theory is conceptually simple and SRCC with singles, doubles and perturbative inclusion of triples excitation --the CCSD(T) method-- has established itself as the 'Gold Standard' in Quantum Chemistry. While there are more rigorous and robust methods, like multi-reference coupled cluster (MRCC) theory, the CCSD(T) remains a popular choice owing to its simplicity in structure. However, due to the steep scaling of the CCSD(T) method, achieving similar accuracy to MRCC with both structural simplicity and a lower scaling behavior remains an important area of research to handle large systems. Introducing the key concepts of SRCC and MRCC, I shall demonstrate how our recently developed methodology, which is termed as "iterative n-body excitation inclusive CCSD", bridges this gap. It accomplishes this by incorporating the essence of MR formalism into a simplified SR method. In my presentation, interesting application to molecules and dispersion bound complexes such as Hydrazine, Pyridine, Peptide-dimers etc. shall also be presented, which will clearly demonstrate the superiority of our current low scaling method against the 'Gold-Standard', while bypassing the difficulty of its high scaling and the complexity of MR structures. Finally, I shall conclude with a roadmap to handle strongly correlated molecular systems.
日時: 2018年2月14日(水)、15:30 – 16:30
場所: AICS 6階講堂
・講演題目：Beyond the Gold-Standard in Quantum Chemistry: An Efficient Single-reference Coupled Cluster Theory, with Multi-reference Correlation Effects, for Molecular Energetics and Spectra