密度泛函理论计算中驯服未结合阴离子的泛函外推
Functional extrapolations to tame unbound anions in density-functional theory calculations
摘要：
密度泛函理论（DFT）计算的标准方法由于自相互作用误差大而不能描述阴离子。这个问题可以通过使用缩小尺寸的定域基组来规避，不留下额外电子离域的可变灵活性。另外，最近的一种方法，利用DFT评估的总能量优化的Hartree-Fock（HF）水平的电子密度已被报道，表明自相互作用的HF密度能够导致一个改进的描述的额外的电子，返回密切符合实验的亲和力。然而，当HF密度太不准确时，这种方法可能失败。在这里，提出了一种替代方法，其中使用嵌入环境来稳定束缚构型中的阴离子。类似的HF的情况下，当计算总能量在DFT水平上对这些校正的密度，电子亲合势在非常好的协议与实验可以恢复。环境的影响可以通过将结果外推到消失嵌入的极限来评估和去除。此外，该方法可以很容易地应用于DFT计算与离域基组，例如平面波，替代的方法是不可行的或更多的计算要求。因此，建议的外推策略也可以适用于扩展系统，经常在凝聚态物理和材料科学研究，我们说明了如何嵌入环境可以利用来确定吸附阴离子的能量-这里是一个氯离子在金属表面-其电荷配置将被错误地预测标准密度泛函。
英文摘要：
Standard flavors of density-functional theory (DFT) calculations are known to fail in describing anions, due to large self-interaction errors. The problem may be circumvented by using localized basis sets of reduced size, leaving no variational flexibility for the extra electron to delocalize. Alternatively, a recent approach exploiting DFT evaluations of total energies on electronic densities optimized at the Hartree-Fock (HF) level has been reported, showing that the self-interaction-free HF densities are able to lead to an improved description of the additional electron, returning affinities in close agreement with the experiments. Nonetheless, such an approach can fail when the HF densities are too inaccurate. Here, an alternative approach is presented, in which an embedding environment is used to stabilize the anion in a bound configuration. Similarly to the HF case, when computing total energies at the DFT level on these corrected densities, electron affinities in very good agreement with experiments can be recovered. The effect of the environment can be evaluated and removed by an extrapolation of the results to the limit of vanishing embedding. Moreover, the approach can be easily applied to DFT calculations with delocalized basis sets, e.g. plane-waves, for which alternative approaches are either not viable or more computationally demanding. The proposed extrapolation strategy can be thus applied also to extended systems, as often studied in condensed-matter physics and materials science, and we illustrate how the embedding environment can be exploited to determine the energy of an adsorbing anion - here a chloride ion on a metal surface - whose charge configuration would be incorrectly predicted by standard density functionals.
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