title: The Significance of Parameters in Charge Equilibration Models.
abstract: Charge equilibration models such as the electronegativity equalization method (EEM) and the split charge equilibration (SQE) are extensively used in the literature for the efficient computation of accurate atomic charges in molecules. However, there is no consensus on a generic set of optimal parameters, even when one only considers parameters calibrated against atomic charges in organic molecules. In this work, the origin of the disagreement in the parameters is investigated by comparing and analyzing six sets of parameters based on two sets of molecules and three calibration procedures. The resulting statistical analysis clearly indicates that the conventional least-squares cost function based solely on atomic charges is in general ill-conditioned and not capable of fixing all parameters in a charge-equilibration model. Methodological guidelines are formulated to improve the stability of the parameters. Although in this case a simple interpretation of individual parameters is not possible, charge equilibration models remain of great practical use for the computation of atomic charges.
authors.affiliation: Center for Molecular Modeling, QCMM Alliance Ghent-Brussels, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium.
authors.forename: T
authors.initials: T
authors.lastname: Verstraelen
authors.affiliation: Department of Inorganic and Physical Chemistry, QCMM Alliance Ghent-Brussels, Ghent University, Krijgslaan 281 (S-3), B-9000 Gent, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Bultinck
authors.affiliation: Center for Molecular Modeling, QCMM Alliance Ghent-Brussels, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: Van Speybroeck
authors.affiliation: Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada.
authors.forename: P W
authors.initials: PW
authors.lastname: Ayers
authors.affiliation: Center for Molecular Modeling, QCMM Alliance Ghent-Brussels, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Van Neck
authors.affiliation: Center for Molecular Modeling, QCMM Alliance Ghent-Brussels, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Waroquier