title: Direct calculation of electron transfer parameters through constrained density functional theory.
abstract: It is shown that constrained density functional theory (DFT) can be used to access diabatic potential energy surfaces in the Marcus theory of electron transfer, thus providing a means to directly calculate the driving force and the inner-sphere reorganization energy. We present in this report an analytic expression for the forces in constrained DFT and their implementation in geometry optimization, a prerequisite for the calculation of electron transfer parameters. The method is then applied to study the symmetric mixed-valence complex tetrathiafulvalene-diquinone radical anion, which is observed experimentally to be a Robin-Day class II compound but found by DFT to be in class III. Constrained DFT avoids this pitfall of over-delocalization and provides a way to find the charge-localized structure. In another application, driving forces and inner-sphere reorganization energies are calculated for the charge recombination (CR) reactions in formanilide-anthraquinone (FA-AQ) and ferrocene-formanilide-anthraquinone (Fc-FA-AQ). While the two compounds have similar reorganization energies, the driving force in FA-AQ is 1 eV larger than in Fc-FA-AQ, in agreement with experimental observations and supporting the experimental conclusion that the anomalously long-lived FA-AQ charge-separated state arises because the electron transfer is in the Marcus inverted region.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Wu
authors.forename: Troy
authors.initials: T
authors.lastname: Van Voorhis
mesh_terms: D000838:Anions / Q000737:chemistry; D000880:Anthraquinones / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry; D005559:Formamides / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D000075163:Metallocenes; D008958:Models, Molecular; D015394:Molecular Structure
chemical_list: D000838:Anions; D000880:Anthraquinones; D016227:Benzoquinones; D005296:Ferrous Compounds; D005559:Formamides; D005609:Free Radicals; D000075163:Metallocenes; C045976:N-phenylformamide; C004532:quinone; C004998:ferrocene