3 years ago

Cluster size convergence for the energetics of the oxygen evolving complex in PSII

Cluster size convergence for the energetics of the oxygen evolving complex in PSII
Per E. M. Siegbahn, Xichen Li
Density functional theory calculations have been made to investigate the stability of the energetics for the oxygen evolving complex of photosystem II. Results published elsewhere have given excellent agreement with experiments for both energetics and structures, where many of the experimental results were obtained several years after the calculations were done. The computational results were obtained after a careful extension from small models to a size of about 200 atoms, where stability of the results was demonstrated. However, recently results were published by Isobe et al., suggesting that very different results could be obtained if the model was extended from 200 to 340 atoms. The present study aims at understanding where this difference comes from. © 2017 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc. By a cluster convergence study, it is shown that the ground state of S3 has an hydroxide in the cube, not an oxyl radical as recently suggested. Six clusters from 200 atoms to 340 atoms have been studied and the energy difference is quite stable at about 15 kcal/mol. There is no indication that the larger clusters should have a different ground state. Overall, it is here emphasized that results for a large cluster needs to be accompanied by a cluster convergence study to be meaningful.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jcc.24863

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