Near edge X‐ray absorption fine structure (NEXAFS) spectra and their pump‐probe extension (PP‐NEXAFS) offer insights into valence‐ and core‐excited states. We present PSIXAS, a recent implementation for simulating NEXAFS and PP‐NEXAFS spectra by means of the transition‐potential and the Δ‐Kohn–Sham method. The approach is implemented in form of a software plugin for the Psi4 code, which provides access to a wide selection of basis sets as well as density functionals. We briefly outline the theoretical foundation and the key aspects of the plugin. Then, we use the plugin to simulate PP‐NEXAFS spectra of thymine, a system already investigated by others and us. It is found that larger, extended basis sets are needed to obtain more accurate absolute resonance positions. We further demonstrate that, in contrast to ordinary NEXAFS simulations, where the choice of the density functional plays a minor role for the shape of the spectrum, for PP‐NEXAFS simulations the choice of the density functional is important. Especially hybrid functionals (which could not be used straightforwardly before to simulate PP‐NEXAFS spectra) and their amount of “Hartree‐Fock like” exact exchange affects relative resonance positions in the spectrum.

中文翻译：

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PSIXAS：基于跃迁电位和 Δ-Kohn-Sham 方法有效模拟 X 射线吸收光谱的 Psi4 插件

近边 X 射线吸收精细结构 (NEXAFS) 光谱及其泵浦探针扩展 (PP-NEXAFS) 提供了对价态和核激发态的见解。我们提出了 PSIXAS，这是一种通过跃迁电位和 Δ-Kohn-Sham 方法模拟 NEXAFS 和 PP-NEXAFS 光谱的最新实现。该方法以 Psi4 代码的软件插件的形式实现，它提供了对多种基组和密度泛函的访问。我们简要概述了插件的理论基础和关键方面。然后，我们使用插件来模拟胸腺嘧啶的 PP-NEXAFS 光谱，这是其他人和我们已经研究过的系统。发现需要更大的扩展基组来获得更准确的绝对共振位置。我们进一步证明，与普通的 NEXAFS 模拟相比，其中密度泛函的选择对光谱形状的影响较小，对于 PP-NEXAFS 模拟，密度泛函的选择很重要。特别是混合泛函（之前不能直接用于模拟 PP-NEXAFS 光谱）及其“类似 Hartree-Fock”的精确交换量会影响光谱中的相对共振位置。