Attosecond X-ray Diffraction Triggered by Core or Valence Ionization of a Dipeptide,Journal of Chemical Theory and Computation

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Attosecond X-ray Diffraction Triggered by Core or Valence Ionization of a Dipeptide
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2017-12-06 00:00:00 , DOI: 10.1021/acs.jctc.7b00920
Daeheum Cho _{1,

2} , Jérémy R. Rouxel ₁ , Markus Kowalewski ₁ , Jin Yong Lee ₃ , Shaul Mukamel ₁

Affiliation

With the advancement of intense ultrafast X-ray sources, it is now possible to create a molecular movie by following the electronic dynamics in real time and real space through time-resolved X-ray diffraction. Here we employ real-time time-dependent density functional theory (RT-TDDFT) to simulate the electronic dynamics after an impulse core or valence ionization in the glycine–phenylalanine (GF) dipeptide. The time-evolving dipole moment, the charge density, and the time-resolved X-ray diffraction signals are calculated. The charge oscillation is calculated for 7 fs for valence ionization and 500 as for core ionization. The charge oscillation time scale is comparable to that found in a phenylalanine monomer (4 fs) [ Science 2014, 346, 336] and is slightly longer because of the elongated glycine chain. Following valence ionization, the charge migration across the GF is mediated by the delocalized lone-pair orbitals of oxygen and nitrogen of the electron-rich amide group. The temporal Fourier transform of the dipole moment provides detailed information on the charge migration dynamics and the molecular orbitals involved. Heterodyne-detected attosecond X-ray diffraction signals provide the magnitude and phase of the scattering amplitude in momentum space and can thus be inverted to yield the charge density in real space.

中文翻译：

二肽核或价电离引发的亚秒级X射线衍射

随着高强度超快X射线源的发展，现在可以通过时间分辨X射线衍射实时跟踪电子动力学，从而制作分子电影。在这里，我们采用实时时变密度泛函理论（RT-TDDFT）来模拟甘氨酸-苯丙氨酸（GF）二肽中的脉冲核心或化合价电离后的电子动力学。计算随时间变化的偶极矩，电荷密度和时间分辨的X射线衍射信号。对于价电离，电荷振荡计算为7 fs，对于核心电离，电荷振荡计算为500 fs。电荷振荡时间刻度相当于在一个苯丙氨酸单体实测值（4个FS）[科学 2014，346，336]，并且由于甘氨酸链的延长而略长。价化电离后，电荷穿过GF的迁移是由富电子酰胺基团的氧和氮的离域孤对轨道所介导的。偶极矩的时间傅立叶变换提供了有关电荷迁移动力学和涉及的分子轨道的详细信息。外差检测到的阿秒X射线衍射信号提供了动量空间中散射幅度的大小和相位，因此可以反转以产生真实空间中的电荷密度。

更新日期：2017-12-06

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