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Videos de Conceptos Relacionados

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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 one, the...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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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.
2.4K
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

1.3K
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
1.3K
Nuclear Overhauser Enhancement (NOE)01:06

Nuclear Overhauser Enhancement (NOE)

1.5K
Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
1.5K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.6K
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...
1.6K
Second Uniqueness Theorem01:16

Second Uniqueness Theorem

2.7K
Consider a region consisting of several individual conductors with a definite charge density in the region between these conductors. The second uniqueness theorem states that if the total charge on each conductor and the charge density in the in-between region are known, then the electric field can be uniquely determined.
In contrast, consider that the electric field is non-unique and apply Gauss's law in divergence form in the region between the conductors and the integral form to the surface...
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Video Experimental Relacionado

Updated: Feb 20, 2026

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Published on: June 7, 2018

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Derivados nucleares analíticos de segundo orden para incrustación de densidad congelada que emplea métodos de campo

Maximilian L Kronenberger1, Sebastian Höfener1

  • 1Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), P.O. Box 6980, 76049 Karlsruhe, Germany.

The Journal of chemical physics
|February 18, 2026
PubMed
Resumen

Este estudio presenta derivados nucleares analíticos de segundo orden para la incrustación de densidad congelada no acoplada (FDEu) en química cuántica. El método calcula con precisión las frecuencias vibracionales para sistemas moleculares grandes, ayudando en los estudios de transporte de carga.

Palabras clave:
incrustación de densidad congeladaderivados nucleares de segundo ordenfrecuencias vibracionalesquímica cuánticatransporte de carga

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Sus antecedentes:

  • El cálculo preciso de las vibraciones moleculares es crucial para comprender las reacciones químicas y las propiedades de los materiales.
  • La incrustación de densidad congelada (FDE) ofrece una forma computacionalmente eficiente de estudiar sistemas grandes al incrustar un subsistema en un entorno más grande.
  • Los gradientes y Hessians analíticos son esenciales para la optimización de geometrías y el análisis vibracional.

Conclusiones:

  • El método FDEu desarrollado proporciona un enfoque preciso y eficiente para calcular frecuencias vibracionales en sistemas moleculares grandes.
  • Este método tiene un potencial significativo para analizar vibraciones intermoleculares relevantes para fenómenos de transporte de carga.
  • El estudio valida las fortalezas y limitaciones de FDEu para diversos entornos químicos.