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arXiv 1508.07580physics.chem-phphysics.atom-ph
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用系综推广方法消除Kohn-Sham密度泛函理论中的渐近分数解离问题

Elimination of the asymptotic fractional dissociation problem in Kohn-Sham density functional theory using the ensemble-generalization approach

Eli Kraisler, Leeor Kronik

摘要:

密度泛函理论中的许多近似都错误地预言,多电子系统可以离解成分数电荷碎片。在这里,我们重新审视解离双原子分子的情况下,已知表现出这个问题时,在标准的方法,包括本地自旋密度近似(LSDA)的研究。通过使用我们最近提出的[E。Kraisler和L. Kronik,Phys. Rev. Lett. 110,126403(2013)]整体推广,我们发现,渐近分数解离被消除在所有系统检查,即使潜在的交换相关性(xc)仍然是LSDA。此外,由于系综推广程序,Kohn-Sham势发展的空间步骤之间的解离原子,反映了出现的衍生物的xc能量泛函的不连续性。这一步,在过去预测的精确科恩-沙姆潜力和观察到的一些更先进的近似形式,是一个理想的功能,防止任何分数之间的电荷转移系统的片段。人们通常认为,简单的xc近似,如LSDA不能发展这一步。然而,我们的研究结果表明,集成推广到分数电子密度自动引入所需的步骤,甚至最简单的近似xc泛函和正确预测渐近整数离解。

英文摘要:

Many approximations within density-functional theory spuriously predict that a many-electron system can dissociate into fractionally charged fragments. Here, we revisit the case of dissociated diatomic molecules, known to exhibit this problem when studied within standard approaches, including the local spin-density approximation (LSDA). By employing our recently proposed [E. Kraisler and L. Kronik, Phys. Rev. Lett. 110, 126403 (2013)] ensemble-generalization we find that asymptotic fractional dissociation is eliminated in all systems examined, even if the underlying exchange-correlation (xc) is still the LSDA. Furthermore, as a result of the ensemble generalization procedure, the Kohn-Sham potential develops a spatial step between the dissociated atoms, reflecting the emergence of the derivative discontinuity in the xc energy functional. This step, predicted in the past for the exact Kohn-Sham potential and observed in some of its more advanced approximate forms, is a desired feature that prevents any fractional charge transfer between the system's fragments. It is usually believed that simple xc approximations such as the LSDA cannot develop this step. Our findings show, however, that ensemble generalization to fractional electron densities automatically introduces the desired step even to the most simple approximate xc functionals and correctly predicts asymptotic integer dissociation.

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