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相关概念视频

Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

1.1K
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
1.1K
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

381
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
381
Valence Bond Theory02:42

Valence Bond Theory

9.2K
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...
9.2K
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

1.0K
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...
1.0K
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

1.1K
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
1.1K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.1K
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...
1.1K

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Updated: Sep 9, 2025

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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旋转适应的反转时间依赖密度函数理论

Chima S Chibueze1, Lucas Visscher1

  • 1Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.

The Journal of chemical physics
|September 4, 2025
PubMed
概括
此摘要是机器生成的。

这项研究引入了新的自旋适应反转时间依赖密度函数理论 (SFD-TD-DFT) 方法,以准确计算高自旋分子系统中的低电子激发. 新的受限开Kohn-Sham (ROKS) 方法为旋转翻转转换提供了更高的精度.

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科学领域:

  • 计算化学
  • 量子力学
  • 理论光谱学

背景情况:

  • 在费米水平的轨道退化系统经常表现出高旋转的基本状态.
  • 通过旋转转向下转换可以访问具有较低总旋转的低水平电子激发.
  • 精确计算这些回转激发对于理解分子性质至关重要.

研究的目的:

  • 开发和介绍三个自旋适应的自旋倒置时间依赖密度函数理论 (SFD-TD-DFT) 方法.
  • 从高旋转基本状态计算电子转换的激发能量.
  • 调查旋转适应和内核描述在这些计算中的作用.

主要方法:

  • 在Tamm-Dancoff近似 (TDA) 中开发基于受限开Kohn-Sham (ROKS) 公式的三种SFD-TD-DFT方法.
  • 在工作方程的核心中使用不同的两电子合元件.
  • 引入了完全自旋适应的ROKS-SFD-TDA方法,这些方法来自单次激发的配置相互作用 (SF-CIS) 和运动方程替代物 (SF-TDA).

主要成果:

  • 不对线核描述对于精确计算旋转反转激发是必不可少的.
  • 完全自旋适应的方法 (SF-CIS和SF-TDA) 可以导致对应效应的人工双重计数.
  • 准旋转适应的SF-TDA (Q-SF-TDA) 方法表现出与旋转不受限制的SFD-TD-DFT可比的稳定性,效率和性能.

结论:

  • 开发的ROKS-SFD-TDA方法为高旋转系统的旋转转换提供精确的激发能量.
  • Q-SF-TDA方法为研究这些电子激发提供了强大而高效的方法.
  • 这些进展有助于更好地理解退化系统中的电子结构和光谱学.