Partial Charge - Determining Partial Atomic Charges

Determining Partial Atomic Charges

Despite its usefulness, the concept of a partial atomic charge is somewhat arbitrary, because it depends on the method used to delimit between one atom and the next (in reality, atoms have no clear boundaries). As a consequence, there are many methods for estimating the partial charges. According to Cramer (2002), all methods can be classified in one of four classes:

  • Class I charges are those that are not determined from quantum mechanics, but from some intuitive or arbitrary approach. These approaches can be based on experimental data such as dipoles and electronegativities.
  • Class II charges are derived from partitioning the molecular wave function using some arbitrary, orbital based scheme.
  • Class III charges are based on a partitioning of a physical observable derived from the wave function, such as electron density.
  • Class IV charges are derived from a semiempirical mapping of a precursor charge of type II or III to reproduce experimentally determined observables such as dipole moments.

The following is a detailed list of methods, partly based on Meister and Schwarz (1994).

  • Population analysis of wavefunctions
    • Mulliken population analysis
    • Coulson's charges
    • Natural charges
    • CM1, CM2, CM3 charge models
  • Partitioning of electron density distributions
    • Bader charges (obtained from an atoms in molecules analysis)
    • Density fitted atomic charges
    • Hirshfeld charges
    • Maslen's corrected Bader charges
    • Politzer's charges
    • Voronoi Deformation Density charges
    • Density Derived Electrostatic and Chemical (DDEC) charges, which simultaneously reproduce the chemical states of atoms in a material and the electrostatic potential surrounding the material's electron density distribution
  • Charges derived from dipole-dependent properties
    • Dipole charges
    • Dipole derivative charges, also called atomic polar tensor (APT) derived charges, or Born, Callen, or Szigeti effective charges
  • Charges derived from electrostatic potential
    • Chelp
    • ChelpG (Breneman model)
    • Merz-Singh-Kollman (also known as Merz-Kollman, or MK)
  • Charges derived from spectroscopic data
    • Charges from infrared intensities
    • Charges from X-ray photoelectron spectroscopy (ESCA)
    • Charges from X-ray emission spectroscopy
    • Charges from X-ray absorption spectra
    • Charges from ligand-field splittings
    • Charges from UV-vis intensities of transition metal complexes
    • Charges from other spectroscopies, such as NMR, EPR, EQR
  • Charges from other experimental data
    • Charges from bandgaps or dielectric constants
    • Apparent charges from the piezoelectric effect
    • Charges derived from adiabatic potential energy curves
    • Electronegativity-based charges
    • Other physicochemical data, such as equilibrium and reaction rate constants, thermochemistry, and liquid densities.
  • Formal charges

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