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arXiv 0904.4560physics.chem-phcond-mat.other
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电荷约束密度泛函分子动力学模拟凝聚相电子转移反应

Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions

H. Oberhofer, J. Blumberger

摘要:

提出了一种基于平面波基组的电荷约束密度泛函分子动力学(CDFT-MD)方法,用于模拟凝聚相体系中的电子转移反应。根据Wu等人的早期工作,Phys.Rev.A72,024502(2005),在供体和受体之间的电荷差等于给定值的约束下,使密度泛函最小化。经典离子动力学在电荷约束态的Born-Oppenheimer面上传播。我们调查的约束能量和能隙的电荷的定义上的依赖关系,并提出表达式的约束力。将该方法应用于水溶液中Ru ~(2+)-Ru ~(3+)的电子自交换反应。沿CDFT-MD轨迹对垂直能隙进行采样,并对有限尺寸效应进行校正,获得1.6 eV的重组自由能。这是0.1-0.2电子伏特低于先前的估计的基础上连续模型的溶剂化。重组自由能的较小值可以通过以下事实来解释:二价和三价Ru-六水合物的Ru-O距离被预测为在电子转移络合物中比分离的水离子更相似。

英文摘要:

We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following earlier work of Wu et al. Phys. Rev. A 72, 024502 (2005), the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge, and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories, and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. smaller value for reorganization free energy can be explained by fact that the Ru-O distances of the divalent and trivalent Ru-hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua-ions.

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