系综密度泛函理论中的密度驱动关联：来自原子简单激发的见解
Density driven correlations in ensemble density functional theory: insights from simple excitations in atoms
摘要：
包合密度泛函理论将通常的Kohn-Sham机制扩展到涉及基态和激发态的量子态系综。最近的工作由作者[物理。119，243001（2017）; 123，016401（2019）]已经表明，哈特里交换能和相关能都可以在系综中获得不寻常的特征。密度驱动（DD）相关性--它解释了Kohn-Sham系综中的纯态密度不一定再现相互作用纯态的密度--就是这样一个特征。在这里，我们研究原子（特别是$S$-$P$和$S$ -$S$过渡），并表明DD相关的幅度和行为可以随所涉及的状态的轨道角动量的变化而变化很大。这样的估计是通过近似DD相关性建立从相关的精确条件Kohn-Sham反演，和合理的假设弱相关系统。
英文摘要：
Ensemble density functional theory extends the usual Kohn-Sham machinery to quantum state ensembles involving ground- and excited states. Recent work by the authors [Phys. Rev. Lett. 119, 243001 (2017); 123, 016401 (2019)] has shown that both the Hartree-exchange and correlation energies can attain unusual features in ensembles. Density-driven(DD) correlations -- which account for the fact that pure-state densities in Kohn-Sham ensembles do not necessarily reproduce those of interacting pure states -- are one such feature. Here we study atoms (specifically $S$--$P$ and $S$--$S$ transitions) and show that the magnitude and behaviour of DD correlations can vary greatly with the variation of the orbital angular momentum of the involved states. Such estimations are obtained through an approximation for DD correlations built from relevant exact conditions Kohn-Sham inversion, and plausible assumptions for weakly correlated systems.
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