How Much Can Density Functional Approximations (DFA) Fail? The Extreme Case of the FeO4 Species

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• 作者：Wei Huang ; Deng-Hui Xing ; Jun-Bo Lu ; Bo Long ; W. H. Eugen Schwarz ; Jun Li
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2016
• 出版时间：April 12, 2016
• 年：2016
• 卷：12
• 期：4
• 页码：1525-1533
• 全文大小：485K
• 年卷期：0
• ISSN：1549-9626

文摘

A thorough theoretical study of the relative energies of various molecular Fe·4O isomers with different oxidation states of both Fe and O atoms is presented, comparing simple Hartree–Fock through many Kohn–Sham approximations up to extended coupled cluster and DMRG multiconfiguration benchmark methods. The ground state of Fe·4O is a singlet, hexavalent iron(VI) complex ¹C_2v-[Fe(VI)O₂]²⁺(O₂)^2–, with isomers of oxidation states Fe(II), Fe(III), Fe(IV), Fe(V), and Fe(VIII) all lying slightly higher within the range of 1 eV. The disputed existence of oxidation state Fe(VIII) is discussed for isolated FeO₄ molecules. Density functional theory (DFT) at various DF approximation (DFA) levels of local and gradient approaches, Hartree–Fock exchange and meta hybrids, range dependent, DFT–D and DFT+U models do not perform better for the relative stabilities of the geometric and electronic Fe·4O isomers than within 1–5 eV. The Fe·4O isomeric species are an excellent testing and validation ground for the development of density functional and wave function methods for strongly correlated multireference states, which do not seem to always follow chemical intuition.