核价分离近似误差的量化
Quantifying the error of the core-valence separation approximation
摘要：
在计算X射线吸收光谱探测的核激发态时，核价分离（CVS）方案已成为一个重要的工具。这种方法允许以高特异性靶向这样的状态，尽管引入了误差。我们报告的实施后处理步骤的CVS激发内的代数图解构造方案的极化传播（ADC），消除了这个错误。在此基础上，我们提供了一个详细的CVS计划的分析，确定其准确性是由两个被忽视的耦合，一个核心和价单激发之间的误差平衡，一个单和双核心之间的激发。的基组的选择是至关重要的适当的描述，这两个耦合，紧极化功能是必要的一个良好的平衡的错误。CVS误差被证实在多个系统中是稳定的，$K$边缘谱计算的元素特异性扩展约为$\pm$ 0.02 eV。一个系统的CVS误差降低0.02-0.03 eV时，注意到考虑激发极端扩散状态，模拟电离。
英文摘要：
For the calculation of core-excited states probed through X-ray absorption spectroscopy, the core-valence separation (CVS) scheme has become a vital tool. This approach allows to target such states with high specificity, albeit introducing an error. We report the implementation of a post-processing step for CVS excitations obtained within the algebraic-diagrammatic construction scheme for the polarisation propagator (ADC), which removes this error. Based on this we provide a detailed analysis of the CVS scheme, identifying its accuracy to be dominated by an error balance between two neglected couplings, one between core and valence single excitations and one between single and double core excitations. The selection of the basis set is shown to be vital for a proper description of both couplings, with tight polarising functions being necessary for a good balance of errors. The CVS error is confirmed to be stable across multiple systems, with an element-specific spread for $K$-edge spectrum calculations of about $\pm$0.02 eV. A systematic lowering of the CVS error by 0.02-0.03 eV is noted when considering excitations to extremely diffuse states, emulating ionisation.
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