title: Note: Energy convexity and density matrices in molecular systems.
abstract: A novel appropriate definition for the density matrix for an interacting Coulombic driven atomic or molecular system with non-integer number of particles is given. Our approach leads to a direct derivation of the proposal reported by Perdew et al. [Phys. Rev. Lett. 49, 1691 (1982)] and points out its suitability and perspective advances.
authors.forename: Roberto C
authors.initials: RC
authors.lastname: Bochicchio
authors.forename: Diego
authors.initials: D
authors.lastname: Rial