Electronic structures of CaMn4O5 cluster in oxygen evolving complex of photosystem II. Theoretical calculations by LPNO-CC methods in the S1 state of the Kok cycle
Takashi Kawakami1,2 , Koichi Miyagawa3 , Hiroshi Isobe4 , Mitsuo Shoji5 , Satoru Yamada3 , Shusuke Yamanaka2 , Mitsutaka Okumura2 , Takahito Nakajima1 , Kizashi Yamaguchi1,2,3,6
1Riken Center for Computational Science, Kobe, Hyogo, 650-0047, Japan
2Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
3The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
4Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
5Center of Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
6NanoScience Design Center, Osaka University, Toyonaka, Osaka 560-8531, Japan
Post-HF molecular orbital calculations of several inorganic model clusters, CaMn4O4XYZ(H2O)2 (X,Y,Z = H2O, OH-, O2-), by using of the LPNO-CC methods were performed in order to illustrate the detailed electronic structures in the catalytic site for water oxidation. Especially, the molecular structures (1aL,1aR,1bC), which were already reported by full geometry optimization by the hybrid DFT (B3LYP) method (H. Isobe et al., Dalton Trans., 41, 13727 (2012)), were modified and used to study the S1 state of the Kok cycle for the oxygen-evolving complex (OEC) of photosystem II (PSII). We have performed the series of LPNO-CC methods as recent development of CC methods in ORCA program package. Here, the reference orbitals to these methods were constructed by the former UB3LYP calculations. The results by using LPNO-CCSD, DLPNO-CCSD and DLPNO-CCSD(T) methods can reveal the performance of electronic correlation correction. In addition, importance of environmental effects such as protein fields were discussed by polarized continuum models (PCM). Finally, relative stabilities of these model clusters were concluded and discussed in relation to the experimental studies.
