Theoretical studies on CaMn4O5 clusters in PSII by high accuracy MO calculations

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05528
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 34010:Inorganic/coordination chemistry-related
• Research Institution: Osaka University
• Principal Investigator: Kawakami Takashi 大阪大学, 大学院理学研究科, 助教 (30321748)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: PSII / CaMn4O5 / hybrid-DFT / LPNO-CC

Outline of Final Research Achievements

Photosystem (PSII) is highly coupled with Mn complexes, which are catalyzed by 'CaMn4O5 clusters'. It belongs to the strongly correlated electron system, and high accuracy MO calculations are required to study electronic properties. Though all the calculations by DFT methods was carried out, more intelligent approaches are essential for elucidating the mechanism of water splitting. We have overcome such limitations by carrying out this study. The UB3LYP calculation with a larger molecular size and the DLPNO-CCSD (T) method as a strongly correlated electronic state calculation technique were carried out in order to perform a highly accurate analysis of each state of the Kok cycle (S0, S1, S2, S3, S4).

Free Research Field

理論化学

Academic Significance and Societal Importance of the Research Achievements

水分解反応を触媒するCaMn4O4XYZWクラスターの分子構造は、実験により解明されている。しかし、実験では水素原子の位置は見えないため、このX,Y,Z,Wが水(H2O)とその酸化誘導体(OH-, O2-)の判別は不能である。そこで、分子軌道法(UB3LYP法)による構造最適化を行い、さらに高精度計算(DLPNO-CCSD(T)法)を実行し先験的に求めた。
Kokサイクル(S0,S1,S2,S3,S4状態)は状態間の遷移によりMnの酸化数が変化していく。それに伴い電子構造も変化し、水分解反応を触媒的に進行する。強相関電子系の理論計算スキームを推進し、DMRG CASCI法の発展を行った。