title: Atomic Charges and the Electrostatic Potential Are Ill-Defined in Degenerate Ground States.
abstract: A system in a spatially degenerate ground state responds in a qualitatively different way to positive and negative point charges. This means that the molecular electrostatic potential is ill-defined for degenerate ground states due to the ill-defined nature of the electron density. It also means that it is impossible, in practice, to define fixed atomic charges for molecular mechanics simulations of molecules with (quasi-)degenerate ground states. Atomic-polarizability-based models and electronegativity-equalization-type models for molecular polarization also fail to capture this effect. We demonstrate the ambiguity in the electrostatic potential using several molecules of different degree of degeneracy, quasi-degeneracy, and symmetry.
authors.affiliation: Department of Inorganic and Physical Chemistry, Ghent University , Krijgslaan 281 (S3), 9000 Gent, Belgium.
authors.forename: Patrick
authors.initials: P
authors.lastname: Bultinck
authors.affiliation: Departamento de Física, Facultad de Ciencias, Universidad de Chile , Casilla 653, Santiago, Chile.|Centro para el desarrollo de la Nanociencias y Nanotecnologia, CEDENNA , Av. Ecuador 3493, Santiago, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Cardenas
authors.affiliation: Departamento de Física, Facultad de Ciencias, Universidad de Chile , Casilla 653, Santiago, Chile.|Centro para el desarrollo de la Nanociencias y Nanotecnologia, CEDENNA , Av. Ecuador 3493, Santiago, Chile.
authors.forename: Patricio
authors.initials: P
authors.lastname: Fuentealba
authors.affiliation: Department of Chemistry & Chemical Biology, McMaster University , Hamilton, Ontario, Canada L8S 4M1.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Johnson
authors.affiliation: Department of Chemistry & Chemical Biology, McMaster University , Hamilton, Ontario, Canada L8S 4M1.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Ayers