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Related Concept Videos

Ionization Energy03:12

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy (IE1). The first ionization energy for an element, X, is the energy required to form a cation with 1+ charge:
Hybridization of Atomic Orbitals II03:35

Hybridization of Atomic Orbitals II

sp3d and sp3d 2 Hybridization
Molecular Orbital Theory II03:51

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams
Chemical Ionization (CI) Mass Spectrometry01:21

Chemical Ionization (CI) Mass Spectrometry

The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
Equilibrium Conditions for a Particle01:23

Equilibrium Conditions for a Particle

When an object is in equilibrium, it is either at rest or moving with a constant velocity. There are two types of equilibrium: static and dynamic. Static equilibrium occurs when an object is at rest, while dynamic equilibrium occurs when an object is moving with a constant velocity. In both cases, there must be a balance of forces acting on the object.
To understand the concept of equilibrium, let us first consider the forces acting on an object. When different forces act on an object, they can...
Mass Analyzers: Common Types01:19

Mass Analyzers: Common Types

The quadrupole mass analyzer consists of four cylindrical metal rods arranged in a diamond carrying a DC voltage and a radio-frequency AC voltage. The motion of ions through the quadrupole depends on the field strength, causing only ions of a certain m/z to resonate successfully and strike the detector at a given field strength. Though the transmission rate for these analyzers is high, the exact elemental composition of the sample is not determined because of low resolution; however, they are...

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Related Experiment Video

Updated: Jul 17, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
05:51

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Published on: July 19, 2019

Higher-order equation-of-motion coupled-cluster methods for ionization processes.

Muneaki Kamiya1, So Hirata

  • 1Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, Florida 32611-8435, USA.

The Journal of Chemical Physics
|September 1, 2006
PubMed
Summary

New equation-of-motion coupled-cluster (EOM-CC) methods accurately calculate ionization potentials. Higher-order calculations like CCSDTQ significantly improve accuracy over simpler methods for molecular systems.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Theoretical Chemistry

Background:

  • Accurate calculation of ionization potentials (IPs) is crucial for understanding molecular electronic structure and reactivity.
  • Traditional methods like IP-EOM-CCSD can exhibit significant errors due to inadequate treatment of orbital relaxation.
  • The development of more sophisticated computational methods is needed to achieve quantitative accuracy in IP predictions.

Purpose of the Study:

  • To derive and implement compact algebraic equations for equation-of-motion coupled-cluster (EOM-CC) methods targeting ionization potentials.
  • To develop and apply parallel algorithms for IP-EOM-CC methods with varying levels of excitation and ionization operator truncation.
  • To assess the accuracy of these methods by comparing theoretical predictions with experimental data for small molecules and radicals.

Main Methods:

  • Development of symbolic algebra systems to automate the derivation of EOM-CC equations.
  • Implementation of parallel algorithms for IP-EOM-CCSD, IP-EOM-CCSDT, and IP-EOM-CCSDTQ methods, incorporating spin, spatial, and permutation symmetries.
  • Application of spin-orbital formalisms to describe various ionization processes from open-shell reference states.

Main Results:

  • IP-EOM-CCSD often shows inadequate orbital relaxation, leading to errors exceeding 2 eV for N2 and CO ionizations.
  • Higher-order methods, IP-EOM-CCSDT and IP-EOM-CCSDTQ, systematically reduce these errors to tenths or hundredths of an eV.
  • Spectroscopic parameters for FH+ and NH+ radicals, including harmonic frequencies and energy separations between electronic states, show improved agreement with experiment using higher-order IP-EOM-CC treatments.

Conclusions:

  • Higher-order equation-of-motion coupled-cluster methods (IP-EOM-CCSDT and IP-EOM-CCSDTQ) are essential for accurate ionization potential calculations.
  • These advanced methods significantly outperform IP-EOM-CCSD, particularly for systems exhibiting substantial orbital relaxation effects.
  • The developed computational tools provide a reliable approach for predicting molecular properties and understanding electronic transitions.