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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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 π orbitals.
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

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 involved orbitals. The...
Reaction Mechanisms: The Steady-State Approximation01:26

Reaction Mechanisms: The Steady-State Approximation

The steady-state approximation, also referred to as the quasi-steady-state approximation to differentiate it from a true steady state, is a widely used method for simplifying calculations in complex reaction mechanisms. This approach is particularly useful when dealing with multi-step reactions that involve reverse reactions or several steps, which can significantly increase mathematical complexity and make the reactions nearly unsolvable analytically.The steady-state approximation operates on...
Debye–Huckel–Onsager Conductance Equation01:28

Debye–Huckel–Onsager Conductance Equation

The Debye-Hückel-Onsager equation is a cornerstone of physical chemistry, providing a method to determine the molar conductance (Λm) and molar conductance at infinite dilution (Λ°m) for uni-univalent electrolytes.Uni-univalent electrolytes are electrolytes that dissociate in solution to produce one cation with a +1 charge and one anion with a –1 charge per formula unit.This equation addresses two crucial phenomena: the asymmetry effect and the electrophoretic effect. According to this equation,...
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Transient and Steady-state Response

In control systems, test signals are essential for evaluating performance under various conditions. The ramp function is effective for systems undergoing gradual changes, while the step function is suitable for assessing systems facing sudden disturbances. For systems subjected to shock inputs, the impulse function is the most appropriate test signal.
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Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...

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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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Published on: May 27, 2020

Nonadiabatic coupling vectors within linear response time-dependent density functional theory.

Ivano Tavernelli1, Enrico Tapavicza, Ursula Rothlisberger

  • 1Laboratory of Computational Chemistry and Biochemistry, Ecole Polytechnique Federale de Lausanne, Lausanne CH-1015, Switzerland. ivano.tavernelli@epfl.ch

The Journal of Chemical Physics
|April 2, 2009
PubMed
Summary
This summary is machine-generated.

Researchers developed a new method to calculate nonadiabatic coupling vectors (NACVs) using time-dependent density functional theory (TDDFT). This efficient approach accurately models excited-state dynamics, crucial for understanding chemical reactions.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Theoretical Chemistry

Background:

  • Nonadiabatic coupling vectors (NACVs) are essential for describing transitions between electronic states in molecules.
  • Accurate computation of NACVs is challenging, particularly for excited states.
  • Previous methods for surface hopping dynamics had limitations in describing excited state wavefunctions.

Purpose of the Study:

  • To develop and validate a new computational method for calculating NACVs.
  • To extend existing surface hopping dynamics methods.
  • To improve the description of excited state wavefunctions within TDDFT.

Main Methods:

  • Linear response time-dependent density functional theory (TDDFT) in the adiabatic approximation.
  • Utilizing linear response orbitals to improve TDDFT excited state wavefunction description.
  • Validation on the H + H(2) system near a conical intersection.
  • Application to protonated formaldimine (NH(2)CH(2)(+)) dynamics.

Main Results:

  • The developed method accurately computes NACVs between ground and excited states, and between excited states.
  • Validation on H + H(2) shows high accuracy comparable to wavefunction-based methods.
  • Numerical efficiency of the approach is confirmed.
  • NACVs were calculated for protonated formaldimine along a surface hopping trajectory.

Conclusions:

  • The new TDDFT-based method provides an accurate and efficient way to compute NACVs.
  • This advancement improves the modeling of excited-state dynamics and chemical reactions.
  • The method is suitable for complex molecular systems and surface hopping simulations.