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相关概念视频

Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

44.8K
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
44.8K
Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

28.0K
Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
28.0K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.0K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
2.0K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.1K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
1.1K
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.2K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.2K
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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一个高效的刺激合方案,基于简化的时间依赖密度功能理论.

Mike Pauls1, Jan Kubelka2, Francesca Plückhahn1

  • 1Institute of Physical Chemistry, RWTH Aachen University, Melatener Str. 20, 52056 Aachen, Germany.

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概括

基于简化的时间依赖密度函数理论 (sTD-DFT) 的新兴子合 (ExC) 方法显著加速了分子聚合物的光谱计算. 这种方法可以在大型系统中快速选光物理性质.

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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.
  • 频谱学是一种光谱学.

背景情况:

  • 精确计算电子吸收和循环二极化谱对于理解分子性质至关重要.
  • 像时间依赖密度函数理论 (TD-DFT) 这样的传统方法对于大型分子系统来说可能是计算上昂贵的.

研究的目的:

  • 开发和介绍一种基于简化的TD-DFT (sTD-DFT) 的高效激子合 (ExC) 方法.
  • 为了快速计算大分子聚合物和软物质的激发光谱.
  • 研究静电嵌入的作用,并使用介电连续体来简化它.

主要方法:

  • 从母 sTD-DFT 方法开发了一种激子合 (ExC) 哈密尔顿式,假设碎片不重叠,忽视断片间的电荷转移.
  • 实施了Tamm-Dancoff近似和随机相位近似自值问题的方法.
  • 研究了使用介电连续体进行静电嵌入,以减少计算复杂性.

主要成果:

  • 与sTD-DFT相比,ExC方法实现了大约两个数量级的计算加速度.
  • 对于高达1万个原子的系统,可以在几分钟内进行计算.
  • 在ExC-sTD-DFT方法复制电子吸收和循环二极化谱,与分离碎片的母体sTD-DFT可比.

结论:

  • 该ExC-sTD-DFT方法提供了一个高效和广泛适用的工具,用于计算分子聚合物的光谱特性.
  • 这种方法有助于在大型分子系统和软物质中选光物理性质.
  • 使用介电连续体进行嵌入进一步提高了计算效率.