Rowan Docs

Fukui Indices and Global Electrophilicity

Python API · stjames models · API example

How it works

Estimate likely reaction sites using atom-centered Fukui indices, and compare molecules' tendency to accept electron density using global electrophilicity. Rowan optionally relaxes the geometry, then compares atomic charges before and after adding or removing an electron at that same geometry.

Settings

  • Optimization level of theory: defaults to GFN2-xTB. Choose a different method to relax the geometry, or select "(Skip)" to use the supplied coordinates. Optimization and Fukui calculations can use different methods.
  • Fukui level of theory: defaults to GFN1-xTB. Other choices include GFN2-xTB and DFT methods such as B97-3c and r²SCAN-3c. The method determines the charge distribution used to calculate the indices.
  • Solvent: available for the Fukui calculation with supported methods; optimization uses gas-phase settings in the web form. Currently, GFN1-xTB and GFN2-xTB Fukui calculations run in the gas phase even if a solvent is selected.

Notes

The input must be a closed-shell singlet molecule. Its starting charge need not be zero: Rowan adds and removes one electron relative to that charge. The charged structures are not separately optimized.

Use the three result views to compare sites within a molecule:

  • "Fukui (positive)" identifies sites susceptible to nucleophilic attack: where the molecule can accept electron density.
  • "Fukui (negative)" identifies sites susceptible to electrophilic attack: where the molecule can donate electron density.
  • "Fukui (zero)" estimates susceptibility to radical attack.

Larger values suggest more responsive sites, but these indices do not predict reaction barriers or account for steric access and reaction conditions. Rankings depend on the geometry, method, basis set, and atomic charge definition. GFN1-xTB uses CM5 charges; GFN2-xTB and DFT calculations use Mulliken charges. Use consistent settings for comparisons.

Global electrophilicity

Global electrophilicity is a whole-molecule descriptor reported in eV; higher values indicate a greater tendency to accept electron density. For DFT, Rowan estimates it from the HOMO and LUMO orbital energies. For xTB, it uses vertical ionization potentials and electron affinities. These are different approximations, so compare values obtained with the same calculation settings.

Submission video

Further reading