Chemistry and Chemical Biology, School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343, USA.
J Chem Phys. 2013 Nov 14;139(18):184116. doi: 10.1063/1.4829642.
Delocalization (or charge-transfer) error is one of the scarce but spectacular failures of density-functional theory. It is particularly apparent in extensively delocalized molecules, and manifests in the calculation of bandgaps, reaction barriers, and dissociation limits. Even though delocalization error is always present in the self-consistent electron density, the differences from reference densities are often quite subtle and the error tends to be driven by the exchange-correlation energy expression. In this article, we propose a model system (the Kevan model) where approximate density functionals predict dramatically different charge distributions because of delocalization error. The model system consists of an electron trapped in a water hexamer and is a finite representation of an experimentally observed class of solids: electrides. The Kevan model is of fundamental interest because it allows the estimation of charge transfer error without recourse to fractional charge calculations, but our results are also relevant in the context of the modeling of confined electrons in density-functional theory.
离域（或电荷转移）误差是密度泛函理论中罕见但显著的失败之一。它在广泛离域的分子中尤为明显，表现在能带隙、反应势垒和离解极限的计算中。尽管离域误差总是存在于自洽电子密度中，但与参考密度的差异通常非常微妙，并且误差往往由交换相关能量表达式驱动。在本文中，我们提出了一个模型系统（Kevan 模型），其中近似密度泛函由于离域误差而预测出截然不同的电荷分布。该模型系统由被困在水分子六聚体中的电子组成，是实验观察到的一类固体（电化物）的有限表示。Kevan 模型具有基本意义，因为它允许在不诉诸分数电荷计算的情况下估计电荷转移误差，但我们的结果在密度泛函理论中对受限电子的建模方面也具有相关性。
