Department of Chemistry and Biochemistry, Wilfrid Laurier University, 75 University Ave. W, Waterloo, Ontario N2L3C5, Canada.
Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, 14476 Potsdam-Golm, Germany.
J Chem Phys. 2018 Oct 14;149(14):144112. doi: 10.1063/1.5050488.
Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is "pumped" by UV or visible light enforcing a valence excitation, followed by an X-ray "probe" exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, method based on density functional theory in combination with the transition potential and ΔSCF methodology (TP-DFT/ΔSCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to → pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to → or → pump/N-K-edge NEXAFS probe spectroscopies of - and -azobenzene.
泵浦探针近边 X 射线吸收精细结构（PP-NEXAFS）谱图可提供价激发态的信息，即使分子本身在光学上是暗的。在 PP-NEXAFS 光谱学中，分子通过紫外或可见光“泵浦”，强制价激发，然后用 X 射线“探针”将芯电子激发到（现在）部分空的价轨道中。到目前为止，PP-NEXAFS 的计算都是通过昂贵的相关波函数方法进行的，这种方法不容易应用于中等大小或大型分子。在这里，我们提出了一种基于密度泛函理论结合跃迁势和 ΔSCF 方法（TP-DFT/ΔSCF）的高效方法，用于计算分子基态和 PP-NEXAFS 谱图。我们将该方法应用于胸腺嘧啶的 → 泵/O-K 边 NEXAFS 探针光谱学（其中存在实验和其他理论数据），以及 - 和 - 偶氮苯的 → 或 → 泵/N-K 边 NEXAFS 探针光谱学。
