Revised force-field parameters for chlorophyll-a, pheophytin-a and plastoquinone-9

•We revised the force-field parameters for three cofactors of photosystem II.•Accurate description of the magnesium water interaction energy in chlorophyll-a.•Structures of chlorophyll-a, pheophytin-a and plastoquinone cores are well described.

Biological photosynthetic machineries, such as photosystem I, photosystem II, or the bacterial reaction center, use cofactor molecules that absorb light or directly participate in chemical reactions. Accurate description of the structure of the cofactors, and of their interactions with protein groups, is an important step toward understanding how photosynthetic machineries work. Here we revisit the classical force field parameters for chlorophyll-a, pheophytin-a and plastoquinone-9. We present systematic quantum mechanical and classical mechanical computations that lead to a good description of the structure and non-bonded interactions of these cofactors.

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