Wu Qin, Van Voorhis Troy
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Phys Chem A. 2006 Jul 27;110(29):9212-8. doi: 10.1021/jp061848y.
It is shown that constrained density functional theory (DFT) can be used to access diabatic potential energy surfaces in the Marcus theory of electron transfer, thus providing a means to directly calculate the driving force and the inner-sphere reorganization energy. We present in this report an analytic expression for the forces in constrained DFT and their implementation in geometry optimization, a prerequisite for the calculation of electron transfer parameters. The method is then applied to study the symmetric mixed-valence complex tetrathiafulvalene-diquinone radical anion, which is observed experimentally to be a Robin-Day class II compound but found by DFT to be in class III. Constrained DFT avoids this pitfall of over-delocalization and provides a way to find the charge-localized structure. In another application, driving forces and inner-sphere reorganization energies are calculated for the charge recombination (CR) reactions in formanilide-anthraquinone (FA-AQ) and ferrocene-formanilide-anthraquinone (Fc-FA-AQ). While the two compounds have similar reorganization energies, the driving force in FA-AQ is 1 eV larger than in Fc-FA-AQ, in agreement with experimental observations and supporting the experimental conclusion that the anomalously long-lived FA-AQ charge-separated state arises because the electron transfer is in the Marcus inverted region.
结果表明，在电子转移的马库斯理论中，约束密度泛函理论（DFT）可用于获取非绝热势能面，从而提供一种直接计算驱动力和内球重组能的方法。在本报告中，我们给出了约束DFT中力的解析表达式及其在几何优化中的实现，这是计算电子转移参数的前提条件。然后将该方法应用于研究对称混合价配合物四硫富瓦烯 - 二醌自由基阴离子，实验观察到该化合物为罗宾 - 戴II类化合物，但DFT计算发现它属于III类。约束DFT避免了过度离域的这个陷阱，并提供了一种找到电荷局域化结构的方法。在另一个应用中，计算了甲酰苯胺 - 蒽醌（FA - AQ）和二茂铁 - 甲酰苯胺 - 蒽醌（Fc - FA - AQ）中电荷复合（CR）反应的驱动力和内球重组能。虽然这两种化合物具有相似的重组能，但FA - AQ中的驱动力比Fc - FA - AQ中的大1 eV，这与实验观察结果一致，并支持了实验结论，即异常长寿命的FA - AQ电荷分离态的出现是因为电子转移处于马库斯反转区域。
