学术讲座
报告题目：Excited states of diradical molecules: towards compact, accurate and insightful wave functions from the Breathing Orbital Valence Bond method
报告时间：2024-10-29 10:00
报告人： Prof. Benoît Braïda
法国索邦大学
报告地点：曾呈奎楼B311
报告摘要：
Calculating excited states properties and transition energies can be a tough task with post-Hartee Fock and traditional multiconfigurational methods for diradicals, even for some small molecules. The difficulties that are encountered are of two kinds: (i) if the ground and excited states are of different symmetries, state-specific calculations can be performed, but it is essential that the correlation energies be calculated in a balanced way for both states. This can be difficult when the two states have very different demands of dynamic electron correlation, e.g., with ionic excited states displaying a lot of dynamic charge fluctuation. (ii) If the two states are of like symmetry, a state-averaged treatment is traditionally used, but the accuracy is penalized by the necessity for both states to share the same orbital set, which is a compromise that cannot be optimal for either of the two states.
These two difficulties are potentially resolved by the Breathing-Orbital Valence Bond method (BOVB), which exerts a direct approach to both static and dynamic electron correlations, made possible by the freedom to deal with non-orthogonal orbitals. The dynamic correlation is fully included right at the orbital optimization step, by allowing each VB structure to have its specific set of orbitals.
The ability of the BOVB method to describe excited states and to compute accurate transition energies with be presented on a few small challenging molecules, using extremely compact of BOVB wave functions (~4-9 valence bond structures in all cases, vs. up to 350 million configurations in valence-CASSCF-MRCISD calculations). Finally, the BOVB description of the excited states is insightful, both regarding the nature of electron correlation in the different states and the chemical interpretation of their electronic structure, displaying some important, albeit unexpected, Lewis structures.
报告人简介：
Benoît Braïda，索邦大学教授，2002年获巴黎第十一大学博士学位，2002-2003年在巴塞罗那自治大学从事博士后工作，自2003年起到2024年8月先后在巴黎第六大学和索邦大学做副教授。主要研究兴趣为化学键理论和量子蒙特卡洛方法等，在J. Am. Chem. Soc., Angewant Chem., Eur. J.等杂志上累计发表文章80余篇。
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