Quantum Chemical Spin Densities for Radical Cations of Photosynthetic Pigment Models
Quantum Chemical Spin Densities for Radical Cations of Photosynthetic Pigment Models
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DOI：
10.1111/php.12757
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发表时间：
2017-05
影响因子：
3.3
通讯作者：
Denis G. Artiukhin;C. Stein;M. Reiher;J. Neugebauer
中科院分区：
文献类型：
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作者：
Denis G. Artiukhin;C. Stein;M. Reiher;J. Neugebauer
采用密度泛函理论和多构型量子化学方法计算了镁卟啉、镁氯和截短叶绿素a模型的自由基阳离子自旋密度。后者可作为近似密度泛函理论的参考，该理论产生的自旋密度可能会受到自相互作用误差的影响。我们通过增加活动轨道空间进行了完整的活动空间自洽场计算，以系统地收敛定性正确的自旋密度。特别是，对于氯镁和叶绿素模型自由基阳离子，这并不容易实现，因为与镁卟啉相比对称性较低。必须采取一些策略，使我们能够考虑非常大的活动轨道空间。我们探索了受限活动空间自洽场和密度矩阵重整化群计算。根据这些参考数据，我们评估了不同密度泛函近似的准确性。我们特别表明，具有正确渐进行为的交换相关模型势能产生良好的自旋密度，并且我们发现，与之前对不同类别化合物的研究一致，混合泛函随着精确交换量的增加而系统地增加自旋极化效应。我们的结果为研究更复杂系统的自旋密度提供了一个起点，例如光系统 II 中主要电子供体的铰链模型。
The spin densities of radical cations of magnesium porphyrin, magnesium chlorine and a truncated chlorophyll a model are calculated with density‐functional theory and multiconfigurational quantum chemical methods. The latter serve as a reference for approximate density‐functional theory which yields spin densities that may suffer from the self‐interaction error. We carried out complete active space self‐consistent field calculations with increasing active orbital spaces to systematically converge qualitatively correct spin densities. In particular, for the magnesium chlorine and chlorophyll a model radical cations, this is not easy to achieve because of the lower symmetry compared to magnesium porphyrin. Strategies had to be employed which allowed us to consider very large active orbital spaces. We explored restricted active space self‐consistent field and density‐matrix renormalization group calculations. Based on these reference data, we assessed the accuracy of different density‐functional approximations. We show that in particular, exchange–correlation model potentials with correct asymptotic behavior yield good spin densities, and we find, in agreement with previous studies on different classes of compounds, that hybrid functionals systematically increase spin‐polarization effects with increasing amounts of exact exchange. Our results provide a starting point for investigations of spin densities of more complex systems such as the hinge model for the primary electron donor in photosystem II.