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相关概念视频

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

990
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
990
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

941
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
941
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.0K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.0K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.4K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
1.4K
Valence Bond Theory02:42

Valence Bond Theory

8.6K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
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双调交换对应函数的混合参考旋转翻转时间依赖密度函数理论.

Konstantin Komarov1, Woojin Park2, Seunghoon Lee3

  • 1Center for Quantum Dynamics, Pohang University of Science and Technology, Pohang 37673, South Korea.

Journal of chemical theory and computation
|October 16, 2023
PubMed
概括
此摘要是机器生成的。

新的交换相关性 (XC) 函数提高了时间依赖密度函数理论 (TDDFT) 计算的准确性. 开发的DTCAM-VEE和DTCAM-AEE功能为激发能量和分子动力学模拟提供了增强的性能.

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科学领域:

  • 计算化学计算化学
  • 量子化学 是一个量子化学.
  • 理论化学 理论化学

背景情况:

  • 准确预测分子性质在计算化学中至关重要.
  • 时间依赖密度函数理论 (TDDFT) 是用于电子结构计算的广泛使用的方法.
  • 开发改进的交换相关性 (XC) 函数是提高TDDFT准确性的关键.

研究的目的:

  • 通过使用不同的XC函数来提高MRSF-TDDFT计算的准确性,用于参考和响应部分.
  • 在库伦减弱框架内基于适应精确交换 (AEE) 概念开发新的XC函数.
  • 评估新函数对垂直激发能量的性能,形交叉点,非相应分子动力学,电荷转移状态和潜在能量表面的性能.

主要方法:

  • 开发了两个新的XC功能:DTCAM-VEE和DTCAM-AEE.
  • 这些函数的应用在多引用第二阶自相一致的时间依赖密度函数理论 (MRSF-TDDFT) 框架内.
  • 根据实验数据和建立的理论基准进行验证,包括蒂尔集和BH&HLYP.
  • 对各种分子系统和属性的性能评估,如激发能,形交叉点,NAMD,电荷转移状态和PES等.

主要成果:

  • DTCAM-VEE与蒂尔的激发能量 (MAE:0.218 eV,IQR:0.327 eV) 集显示出极好的一致性.
  • DTCAM-AEE准确地复制了转二烯和氨酸的形交叉点,以及氨酸的NAMD模拟.
  • 对于电荷转移状态,DTCAM-AEE显示了精确的1/R非对称行为,对于rPSB6模型,也显示了精确的PES.
  • 在BH&HLYP上,DTCAM-AEE显著改善,MAE为0.237 eV,IQR为0.41 eV.

结论:

  • 在参考和响应计算中使用不同的XC函数显著提高了MRSF-TDDFT的准确性.
  • 新开发的DTCAM-VEE和DTCAM-AEE函数为计算化学提供了一个有前途的进步.
  • 该方法为开发可用于各种理论化学问题的改进的XC函数提供了一个新的途径.