从Bethe-Salpeter方程形式理论研究自旋守恒和自旋翻转的光激发
Spin-Conserved and Spin-Flip Optical Excitations From the Bethe-Salpeter Equation Formalism
摘要：
像绝热含时密度泛函理论（TD-DFT）一样，多体微扰理论的贝特-萨尔彼得方程（BSE）形式在其静态近似下对双激发（和更高的激发）是“盲”的，双激发普遍存在于例如共轭分子如多烯中。在这里，我们应用自旋翻转\textit{ansatz}（它认为最低的三重态作为参考配置，而不是单线态基态）的BSE形式主义，以访问，特别是，双激发。本计划是基于自旋不受限制的版本的$GW$近似计算所需的带电荷的激发和屏蔽库仑势的BSE计算。动态校正静态BSE光激发考虑到通过我们最近开发的（重整化）微扰处理的无限制的推广。本自旋翻转BSE形式主义的性能说明通过计算铍原子，氢分子在各种键长的激发态能量，和环丁二烯在其矩形和正方形平面几何形状。
英文摘要：
Like adiabatic time-dependent density-functional theory (TD-DFT), the Bethe-Salpeter equation (BSE) formalism of many-body perturbation theory, in its static approximation, is "blind" to double (and higher) excitations, which are ubiquitous, for example, in conjugated molecules like polyenes. Here, we apply the spin-flip \textit{ansatz} (which considers the lowest triplet state as the reference configuration instead of the singlet ground state) to the BSE formalism in order to access, in particular, double excitations. The present scheme is based on a spin-unrestricted version of the $GW$ approximation employed to compute the charged excitations and screened Coulomb potential required for the BSE calculations. Dynamical corrections to the static BSE optical excitations are taken into account via an unrestricted generalization of our recently developed (renormalized) perturbative treatment. The performance of the present spin-flip BSE formalism is illustrated by computing excited-state energies of the beryllium atom, the hydrogen molecule at various bond lengths, and cyclobutadiene in its rectangular and square-planar geometries.
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