16.4 Calculating Gasteiger Partial Charges

To assign Marsilli-Gasteiger partial charges to a molecule, OEChem provides the OEGasteigerPartialCharges function. This sets the partial charge property of each atom, using the OEAtomBase::SetPartialCharge method. The algorithm itself reproduces the partial charges as calculated by Tripos Inc's Sybyl software, with default parameter settings, which is the de facto reference implementation for Gasteiger charges.

The Gasteiger partial charge algorithm currently assumes that all hydrogen atoms are represented explicitly, for example by calling OEAddExplicitHydrogens.

The current version of OEGasteigerPartialCharges should return the same results independent of the currently assigned aromaticity models and the values of each atom's "integer atom type" property. Early versions of OEChem allowed customization of the Gasteiger charge calculation by explicitly assigning the Tripos atoms types of each atom of the molecule. Unfortunately, this required assigning Tripos' aromaticity and assigning Tripos atom types before each call to OEGasteigerPartialCharges. The more recent behavior is less error-prone (as it's no longer possible to forget to prepare a molecule) and greatly simplifies common usage.

The first stage of the Marsilli-Gasteiger ``Partial Equalization of Orbital Electronegativities (PEOE)'' calculation is assignment of seed charges to each atoms. Typically for neutral atoms the partial charges is seeded zero, but for example, each oxygen in a carboxylate is assigned -0.5, and the net formal charge on conjugated rings is shared equally amongst the atoms of the ring system. These seed charges may also be useful in some applications, and can be assigned using the OEGasteigerInitialCharges method.

				OEChem - C++ Theory Manual Version 1.3.1

				OEChem - C++ Theory Manual Version 1.3.1