Solovyeva Alisa, Pavanello Michele, Neugebauer Johannes
Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
Department of Chemistry, Rutgers University, 73 Warren St., Newark, New Jersey 07102, USA.
J Chem Phys. 2014 Apr 28;140(16):164103. doi: 10.1063/1.4871301.
Long-range charge-transfer processes in extended systems are difficult to describe with quantum chemical methods. In particular, cost-effective (non-hybrid) approximations within time-dependent density functional theory (DFT) are not applicable unless special precautions are taken. Here, we show that the efficient subsystem DFT can be employed as a constrained DFT variant to describe the energetics of long-range charge-separation processes. A formal analysis of the energy components in subsystem DFT for such excitation energies is presented, which demonstrates that both the distance dependence and the long-range limit are correctly described. In addition, electronic couplings for these processes as needed for rate constants in Marcus theory can be obtained from this method. It is shown that the electronic structure of charge-separated states constructed by a positively charged subsystem interacting with a negatively charged one is difficult to converge - charge leaking from the negative subsystem to the positive one can occur. This problem is related to the delocalization error in DFT and can be overcome with asymptotically correct exchange-correlation (XC) potentials or XC potentials including a sufficiently large amount of exact exchange. We also outline an approximate way to obtain charge-transfer couplings between locally excited and charge-separated states.
在扩展体系中，长程电荷转移过程很难用量子化学方法来描述。特别是，在含时密度泛函理论（DFT）中，除非采取特殊措施，否则具有成本效益的（非杂化）近似方法并不适用。在此，我们表明，高效子体系DFT可作为一种受限DFT变体，用于描述长程电荷分离过程的能量学。本文对这类激发能的子体系DFT中的能量成分进行了形式分析，结果表明，距离依赖性和长程极限均得到了正确描述。此外，该方法还可得到Marcus理论中速率常数所需的这些过程的电子耦合。结果表明，由带正电的子体系与带负电的子体系相互作用构建的电荷分离态的电子结构很难收敛，可能会发生电荷从负子体系泄漏到正子体系的情况。这个问题与DFT中的离域误差有关，可以通过渐近正确的交换相关（XC）势或包含足够大量精确交换的XC势来克服。我们还概述了一种获得局域激发态与电荷分离态之间电荷转移耦合的近似方法。
