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相关概念视频

Propagation of Uncertainty from Systematic Error01:10

Propagation of Uncertainty from Systematic Error

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The atomic mass of an element varies due to the relative ratio of its isotopes. A sample's relative proportion of oxygen isotopes influences its average atomic mass. For instance, if we were to measure the atomic mass of oxygen from a sample, the mass would be a weighted average of the isotopic masses of oxygen in that sample. Since a single sample is not likely to perfectly reflect the true atomic mass of oxygen for all the molecules of oxygen on Earth, the mass we obtain from this...
554
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...
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NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

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When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
722
Propagation of Uncertainty from Random Error00:59

Propagation of Uncertainty from Random Error

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An experiment often consists of more than a single step. In this case, measurements at each step give rise to uncertainty. Because the measurements occur in successive steps, the uncertainty in one step necessarily contributes to that in the subsequent step. As we perform statistical analysis on these types of experiments, we must learn to account for the propagation of uncertainty from one step to the next. The propagation of uncertainty depends on the type of arithmetic operation performed on...
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¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
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Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

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In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the...
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定量化 内部分子基础 集合 叠加错误

Quentin Pitteloud1, Peter Wind1, Stig Rune Jensen1

  • 1Hylleraas Centre, Department of Chemistry, UiT the Arctic University of Norway, Tromsø N-9037, Norway.

Journal of chemical theory and computation
|August 18, 2023
PubMed
概括
此摘要是机器生成的。

中等大小的高斯基数组在计算化学中会导致重大错误,人工偏好紧的分子形状. 为了准确的构造分析,需要更大的基础集或多解析度方法.

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科学领域:

  • 计算化学是一种计算化学.
  • 量子化学是一种量子化学.
  • 分子建模分子建模

背景情况:

  • 基础集叠加错误 (BSSE) 是量子化学计算中的一个已知的工件.
  • 准确的结构分析对于理解分子性质和相互作用至关重要.

研究的目的:

  • 在中型高斯基数组中量化分子内基数组叠加错误 (BSSE).
  • 评估在大型分子系统中减轻BSSE的方法.
  • 评估 BSSE 对形状偏好的影响.

主要方法:

  • 进行了哈特里-福克 (HF) 和密度函数理论 (DFT) 的计算.
  • 计算使用了中等大小的高斯基数集 (例如,偏振双色球,偏振三色球).
  • 内部分子BSSE研究了一种186原子的去.
  • 测试了基于多层层的两个BSSE校正程序和多重解析方法.

主要成果:

  • 显著的分子内BSSE (高达~80kJ/mol) 被观察到与极化双泽塔基础集.
  • 误差被减少到~10kJ/mol与极化三倍泽塔基础集.
  • 需要更大的基础集 (极化四倍泽塔) 或多分辨率方法来最大限度地减少BSSE低于几kJ/mol.
  • 在延伸的方面,BSSE人工稳定了紧的形状.

结论:

  • 中等大小的高斯基数组引入了大量的分子内BSSE,影响了构造稳定性.
  • 准确的形状预测需要更大的基础集或先进的技术,如多分辨率方法.
  • 对于大型分子的可靠计算研究,必须仔细处理BSSE.