Aragó Juan, Troisi Alessandro
Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom.
J Chem Phys. 2015 Apr 28;142(16):164107. doi: 10.1063/1.4919241.
In this paper, we present a diabatization scheme to compute the excitonic couplings between an arbitrary number of states in molecular pairs. The method is based on an algebraic procedure to find the diabatic states with a desired property as close as possible to that of some reference states. In common with other diabatization schemes, this method captures the physics of the important short-range contributions (exchange, overlap, and charge-transfer mediated terms) but it becomes particularly suitable in presence of more than two states of interest. The method is formulated to be usable with any level of electronic structure calculations and to diabatize different types of states by selecting different molecular properties. These features make the diabatization scheme presented here especially appropriate in the context of organic crystals, where several excitons localized on the same molecular pair may be found close in energy. In this paper, the method is validated on the tetracene crystal dimer, a well characterized case where the charge transfer (CT) states are closer in energy to the Frenkel excitons (FE). The test system was studied as a function of an external electric field (to explore the effect of changing the relative energy of the CT excited state) and as a function of different intermolecular distances (to probe the strength of the coupling between FE and CT states). Additionally, we illustrate how the approximation can be used to include the environment polarization effect.
在本文中，我们提出了一种绝热态确定方案，用于计算分子对中任意数量状态之间的激子耦合。该方法基于一种代数程序，以找到具有尽可能接近某些参考状态性质的所需性质的绝热态。与其他绝热态确定方案一样，该方法捕捉了重要的短程贡献（交换、重叠和电荷转移介导项）的物理过程，但在存在两个以上感兴趣的状态时，它变得特别适用。该方法的制定使其可用于任何电子结构计算水平，并通过选择不同的分子性质来确定不同类型的状态。这些特性使得本文提出的绝热态确定方案在有机晶体的背景下特别适用，在有机晶体中，可以发现位于同一分子对上的几个激子在能量上很接近。在本文中，该方法在并四苯晶体二聚体上得到了验证，这是一个特征明确的案例，其中电荷转移（CT）态在能量上更接近弗伦克尔激子（FE）。研究了测试系统作为外部电场的函数（以探索改变CT激发态相对能量的影响）以及作为不同分子间距离的函数（以探测FE和CT态之间耦合的强度）。此外，我们还说明了如何使用该近似来包括环境极化效应。
