title: What is an atom in a molecule?
abstract: The derivation of the Hirshfeld atoms in molecules from information theory is clarified. The importance for chemistry of the concept of atoms in molecules (AIM) is stressed, and it is argued that this concept, while highly useful, constitutes a noumenon in the sense of Kant.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27514-3290, USA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Parr
authors.forename: Paul W
authors.initials: PW
authors.lastname: Ayers
authors.forename: Roman F
authors.initials: RF
authors.lastname: Nalewajski