Bruneval Fabien, Sottile Francesco, Olevano Valerio, Reining Lucia
European Theoretical Spectroscopy Facility (ETSF), Laboratoire des Solides Irradiés, UMR 7642, CNRS-CEA/DSM, Ecole Polytechnique, F-91128 Palaiseau, France.
J Chem Phys. 2006 Apr 14;124(14):144113. doi: 10.1063/1.2186996.
In the description of the interaction between electrons beyond the classical Hartree picture, bare exchange often yields a leading contribution. Here we discuss its effect on optical spectra of solids, comparing three different frameworks: time-dependent Hartree-Fock, a recently introduced combined density-functional and Green's function approaches applied to the bare exchange self-energy, and time-dependent exact exchange within time-dependent density-functional theory (TD-EXX). We show that these three approximations give rise to identical excitonic effects in solids; these effects are drastically overestimated for semiconductors. They are partially compensated by the usual overestimation of the quasiparticle band gap within Hartree-Fock. The physics that lacks in these approaches can be formulated as screening. We show that the introduction of screening in TD-EXX indeed leads to a formulation that is equivalent to previously proposed functionals derived from many-body perturbation theory. It can be simulated by reducing the long-range part of the Coulomb interaction: this produces absorption spectra of semiconductors in good agreement with experiment.
在超越经典哈特里图像的电子相互作用描述中，裸交换通常会产生主要贡献。在此，我们讨论其对固体光谱的影响，比较三种不同的框架：含时哈特里 - 福克方法、最近引入的应用于裸交换自能的密度泛函与格林函数相结合的方法，以及含时密度泛函理论（TD - EXX）中的含时精确交换方法。我们表明，这三种近似在固体中产生相同的激子效应；对于半导体，这些效应被严重高估。它们部分地被哈特里 - 福克方法中通常对准粒子带隙的高估所补偿。这些方法中所缺乏的物理机制可以表述为屏蔽。我们表明，在TD - EXX中引入屏蔽确实会导致一种与先前从多体微扰理论导出的泛函等效的表述。它可以通过减小库仑相互作用的长程部分来模拟：这产生的半导体吸收光谱与实验结果吻合良好。
