title: Control of single-molecule junction conductance of porphyrins via a transition-metal center.
abstract: Using scanning tunneling microscope break-junction experiments and a new first-principles approach to conductance calculations, we report and explain low-bias charge transport behavior of four types of metal-porphyrin-gold molecular junctions. A nonequilibrium Green's function approach based on self-energy corrected density functional theory and optimally tuned range-separated hybrid functionals is developed and used to understand experimental trends quantitatively. Importantly, due to the localized d states of the porphyrin molecules, hybrid functionals are essential for explaining measurements; standard semilocal functionals yield qualitatively incorrect results. Comparing directly with experiments, we show that the conductance can change by nearly a factor of 2 when different metal cations are used, counter to trends expected from gas-phase ionization energies which are relatively unchanged with the metal center. Our work explains the sensitivity of the porphyrin conductance with the metal center via a detailed and quantitative portrait of the interface electronic structure and provides a new framework for understanding transport quantitatively in complex junctions involving molecules with localized d states of relevance to light harvesting and energy conversion.
authors.affiliation: Molecular Foundry and Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Zhen-Fei
authors.initials: ZF
authors.lastname: Liu
authors.forename: Sujun
authors.initials: S
authors.lastname: Wei
authors.forename: Hongsik
authors.initials: H
authors.lastname: Yoon
authors.forename: Olgun
authors.initials: O
authors.lastname: Adak
authors.forename: Ingrid
authors.initials: I
authors.lastname: Ponce
authors.forename: Yivan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Woo-Dong
authors.initials: WD
authors.lastname: Jang
authors.forename: Luis M
authors.initials: LM
authors.lastname: Campos
authors.forename: Latha
authors.initials: L
authors.lastname: Venkataraman
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Neaton
keywords: Porphyrins and metalloporphyrins; density functional theory; nonequilibrium Green’s function; range-separated hybrid functional; self-energy correction; single-molecule junction conductance