Department of Physics, University of Houston, Houston, Texas 77204, United States.
Department of Chemistry, Kent State University, Kent, Ohio 44242, United States.
J Chem Theory Comput. 2020 Oct 13;16(10):6481-6490. doi: 10.1021/acs.jctc.0c00796. Epub 2020 Sep 30.
We present a comprehensive analysis of the interplay between the choice of an electronic structure method and the effect of using polarizable force fields vs. nonpolarizable force fields when calculating solution-phase charge-transfer (CT) rates. The analysis is based on an integrative approach that combines inputs from electronic structure calculations and molecular dynamics simulations and is performed in the context of the carotenoid-porphyrin-C molecular triad dissolved in an explicit tetrahydrofuran (THF) liquid solvent. Marcus theory rate constants are calculated for the multiple CT processes that occur in this system based on either polarizable or nonpolarizable force fields, parameterized using density functional theory (DFT) with either the B3LYP or the Baer-Neuhauser-Livshits (BNL) density functionals. We find that the effect of switching from nonpolarizable to polarizable force fields on the CT rates is strongly dependent on the choice of the density functional. More specifically, the rate constants obtained using polarizable and nonpolarizable force fields differ significantly when B3LYP is used, while much smaller changes are observed when BNL is used. It is shown that this behavior can be traced back to the tendency of B3LYP to overstabilize CT states, thereby pushing the underlying electronic transitions to the deep inverted region, where even small changes in the force fields can lead to significant changes in the CT rate constants. Our results demonstrate the importance of combining polarizable force fields with an electronic structure method that can accurately capture the energies of excited CT states when calculating charge-transfer rates.
我们全面分析了在计算溶液相电荷转移（CT）速率时，选择电子结构方法和使用极化力场与非极化力场的效果之间的相互作用。该分析基于一种综合方法，结合了电子结构计算和分子动力学模拟的输入，并在溶解于显式四氢呋喃（THF）液体溶剂中的类胡萝卜素-卟啉-C 分子三联体的背景下进行。根据该体系中发生的多个 CT 过程，基于极化或非极化力场，使用密度泛函理论（DFT）和 B3LYP 或 Baer-Neuhauser-Livshits（BNL）密度泛函参数化，计算了马库斯理论速率常数。我们发现，从非极化力场切换到极化力场对 CT 速率的影响强烈依赖于密度泛函的选择。更具体地说，当使用 B3LYP 时，使用极化和非极化力场获得的速率常数差异很大，而当使用 BNL 时，观察到的变化要小得多。结果表明，这种行为可以追溯到 B3LYP 过度稳定 CT 态的趋势，从而将潜在的电子跃迁推向深反转区域，即使力场发生微小变化也会导致 CT 速率常数发生显著变化。我们的结果表明，在计算电荷转移速率时，将极化力场与能够准确捕获激发 CT 态能量的电子结构方法相结合的重要性。
