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Resonance and Hybrid Structures

Resonance and Hybrid Structures

According to the theory of resonance, if two or more Lewis structures with the same arrangement of atoms can be written for a molecule, ion, or radical, the actual distribution of electrons is an average of that shown by the various Lewis structures.
Resonance Structures and Resonance Hybrids
The Lewis structure of a nitrite anion (NO2−) may actually be drawn in two different ways, distinguished by the locations of the N–O and N=O bonds.

Double Resonance Techniques: Overview

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...

Concept of Resonance and its Characteristics

Concept of Resonance and its Characteristics

If a driven oscillator needs to resonate at a specific frequency, then very light damping is required. An example of light damping includes playing piano strings and many other musical instruments. Conversely, to achieve small-amplitude oscillations as in a car's suspension system, heavy damping is required. Heavy damping reduces the amplitude, but the tradeoff is that the system responds at more frequencies. Speed bumps and gravel roads prove that even a car's suspension system is not immune...

Resonance

Resonance

The Lewis structure of a nitrite anion (NO2−) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O bonds.

Resonance in an AC Circuit

Resonance in an AC Circuit

The property of an inductor makes it resist any change in the current passing through it, while the property of a capacitor is to build up the charge across its terminals. Hence, if an inductor and capacitor are connected in series, they have opposite effects on the relative phase between current and voltage. The current through the circuit undergoes forced oscillation at the frequency of the source. The resistance term in an R-L-C circuit acts as a damping term because power is dissipated...

Valence Bond Theory and Hybridized Orbitals

Valence Bond Theory and Hybridized Orbitals

According to valence bond theory, a covalent bond results when: (1) an orbital on one atom overlaps an orbital on a second atom, and (2) the single electrons in each orbital combine to form an electron pair. The strength of a covalent bond depends on the extent of overlap of the orbitals involved. Maximum overlap is possible when the orbitals overlap on a direct line between the two nuclei.
A σ bond (single bond in a Lewis structure) is a covalent bond in which the electron density is...

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Related Experiment Video

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Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

Published on: August 6, 2018

Autoionizing resonances in time-dependent density functional theory.

August J Krueger¹, Neepa T Maitra

¹Department of Physics and Astronomy, Hunter College and City University of New York, 695 Park Avenue, New York, NY 10065, USA.

Physical Chemistry Chemical Physics : PCCP

|May 29, 2009

Summary

This summary is machine-generated.

Time-dependent density functional theory (TDDFT) approximations accurately capture single-excitation autoionizing resonances but struggle with double excitations. New frequency-dependent kernels are derived to improve TDDFT

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Published on: May 27, 2020

Area of Science:

Quantum Chemistry
Theoretical Chemistry
Computational Physics

Background:

Time-dependent density functional theory (TDDFT) approximations accurately capture single-excitation autoionizing resonances.
Existing TDDFT approximations fail to accurately describe autoionizing resonances arising from bound double excitations.

Purpose of the Study:

To develop improved TDDFT approximations for describing autoionizing resonances from double excitations.
To explain the origin of frequency-dependent resonant structures in TDDFT response functions.

Main Methods:

Derivation of a frequency-dependent kernel as an a posteriori correction to adiabatic approximations in TDDFT.
Development of a "Fano TDDFT kernel" and a "dressed kernel" within the TDDFT formalism.
Testing the derived kernels on a simple model system.

Main Results:

The proposed approximation becomes exact for isolated resonances in the weak interaction limit.
The derived Fano TDDFT kernel reproduces Fano lineshapes within TDDFT.
The study explains how adiabatic kernels can generate frequency-dependent structures for single excitations.

Conclusions:

Frequency-dependent kernels are necessary for accurately describing double-excitation autoionizing resonances in TDDFT.
The derived kernels offer a significant improvement over existing adiabatic approximations.
This work advances the capability of TDDFT for studying complex electronic excitations.