Balancing Exchange Mixing in Density-Functional Approximations for Iron Porphyrin

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• 作者：Victoria E. J. Berryman ; Russell J. Boyd ; Erin R. Johnson
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2015
• 出版时间：July 14, 2015
• 年：2015
• 卷：11
• 期：7
• 页码：3022-3028
• 全文大小：329K
• ISSN：1549-9626

文摘

Predicting the correct ground-state multiplicity for iron(II) porphyrin, a high-spin quintet, remains a significant challenge for electronic-structure methods, including commonly employed density functionals. An even greater challenge for these methods is correctly predicting favorable binding of O₂ to iron(II) porphyrin, due to the open-shell singlet character of the adduct. In this work, the performance of a modest set of contemporary density-functional approximations is assessed and the results interpreted using Bader delocalization indices. It is found that inclusion of greater proportions of Hartree鈥揊ock exchange, in hybrid or range-separated hybrid functionals, has opposing effects; it improves the ability of the functional to identify the ground state but is detrimental to predicting favorable dioxygen binding. Because of the uncomplementary nature of these properties, accurate prediction of both the relative spin-state energies and the O₂ binding enthalpy eludes conventional density-functional approximations.