UNDERSTANDING CHARGE-TRANSFER PHENOMENA IN A CANONICAL ELECTRON DONOR-ACCEPTOR COMPLEX: TETRATHIAFULVALENE (TTF)- TETRACYANOQUINODIMETHANE (TCNQ)

摘要

Recent studies of hybrid layered interfacial systems havenrevealed remarkable electronic, visible light response andn(photo)catalytic properties (e.g., 1). Such properties appear often tonbe intimately related to intrinsic charge transfer properties of thenhybrid interfacial systems in their ground electronic states (e.g., 2,3).nHence, a sound fundamental understanding of charge transfernproperties of complexes and interfaces is an important objective. Innthis work, we make a detailed exploration of the charge transfernproperties of a canonical electron donor-acceptor pair: thenTetrathiafulvalene (TTF)-Tetracyanoquinodimethane (TCNQ) dimer.nOur study shows that the simple frontier-orbital based picture ofnelectron transfer for this system as derived from conventional DFTncalculations is both qualitatively and quantitatively erroneous, in thensense that it rationalizes the experimentally known electronicnproperties for the wrong reasons. A recently developed DFTnapproach that alleviates self-interaction errors (4) is utilized tonillustrate that charge transfer effects in the TTF-TCNQ dimer are notnonly much smaller than predicted by conventional (semi)localnfunctionals such as Perdew-Burke-Ernzerhof (PBE) and local densitynapproximation (LDA), but in addition are highly asymmetric –ndepending sensitively on relative orientation of the two molecules.