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Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package
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Properties and applications of the average interparticle distance.

J W Hollett1, R A Poirier

  • 1Department of Chemistry, Memorial Univeristy of Newfoundland, St. John's, NL A1B 3X7, Canada. jhollett@mun.ca

Journal of Molecular Modeling
|December 18, 2008
PubMed
Summary

First and second moment operators define origin-invariant molecular size and shape. These measures predict steric effects and relate electron-nucleus/electron-electron distances to Hartree-Fock energy components.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Molecular Modeling

Background:

  • Molecular size and shape are crucial for predicting chemical properties and reactivity.
  • Existing methods for quantifying molecular size, such as isodensity contours, have limitations.
  • Understanding electron-electron and electron-nuclear interactions is fundamental to molecular energy calculations.

Purpose of the Study:

  • To introduce a novel method for defining origin-invariant molecular size and shape using moment operators.
  • To establish relationships between these new size measures and experimentally observed steric effects.
  • To correlate average inter-particle distances with fundamental components of the Hartree-Fock energy.

Main Methods:

  • Utilizing first and second moment operators to derive origin-invariant descriptors for molecular size and shape.
  • Calculating average electron-electron and electron-nuclear distances within molecules.
  • Comparing the derived molecular size measure with existing theoretical volume calculations (isodensity contours).
  • Correlating predicted steric effects with experimental data for various substituents.

Main Results:

  • The defined molecular size measure shows good correlation with molecular volume from isodensity contours.
  • The molecular size measure effectively predicts experimentally observed steric effects.
  • Average electron-electron distances correlate well with Coulomb energy, particularly for localized molecular orbitals.
  • Average electron-nuclear distances are closely related to electron-nuclear attraction energy.

Conclusions:

  • First and second moment operators provide robust, origin-invariant measures of molecular size and shape.
  • These measures have predictive power for steric effects and offer insights into molecular energy components.
  • The approach offers a new perspective on quantifying molecular properties relevant to chemical reactivity and interactions.