The Appropriateness of Density‐Functional Theory for the Calculation of Molecular Electronics Properties

Abstract

As molecular electronics advances, efficient and reliable computation procedures are required for the simulation of the atomic structures of actual devices, as well as for the prediction of their electronic properties. Density-functional theory (DFT) has had widespread success throughout chemistry and solid-state physics, and it offers the possibility of fulfilling these roles. In its modern form it is an empirically parameterized approach that cannot be extended toward exact solutions in a prescribed way, ab initio. Thus, it is essential that the weaknesses of the method be identified and likely shortcomings anticipated in advance. We consider four known systematic failures of modern DFT: dispersion, charge transfer, extended pi conjugation, and bond cleavage. Their ramifications for molecular electronics applications are outlined and we suggest that great care is required when using modern DFT to partition charge flow across electrode-molecule junctions, screen applied electric fields, position molecular orbitals with respect to electrode Fermi energies, and in evaluating the distance dependence of through-molecule conductivity. The causes of these difficulties are traced to errors inherent in the types of density functionals in common use, associated with their inability to treat very long-range electron correlation effects. Heuristic enhancements of modern DFT designed to eliminate individual problems are outlined, as are three new schemes that each represent significant departures from modern DFT implementations designed to provide a priori improvements in at least one and possible all problem areas. Finally, fully semiempirical schemes based on both Hartree-Fock and Kohn-Sham theory are described that, in the short term, offer the means to avoid the inherent problems of modern DFT and, in the long term, offer competitive accuracy at dramatically reduced computational costs.

The Manganite−Water Interface

“…Clearly, however, PW91 has been shown to provide an excellent description for most of the properties of manganite and related materials, 3 and it is also known to provide a generally reliable description of liquid water. 17 Unfortunately, DFT approaches are computationally expensive as well as being subject to systematic failures 18 (though no such failure is expected for manganite). A new semiempirical method, Parametrized Model 6 (PM6) introduced by Stewart 19 is currently in its beta development phase.…”

Zero-bias molecular electronics: Exchange-correlation corrections to Landauer's formula

“…In consequence, questions have recently been raised about the validity of the NEGF approach [10,13]. For example, the calculated transmission is that of the KS potential.…”

Anomalous length dependence of the conductance of graphene nanoribbons with zigzag edges

“…The inherent problem of DFT band alignment between the metal contacts and extended conjugated molecule is particularly serious for weakly adsorbed wires with azine anchors. 15,33 In order to rectify the large error in the HOMO-LUMO energy gap in benzene-1,4-diamine, empirical correction has been applied by Quek et al 34 Recently, we have successfully employed the ASIC to partly correct the band alignment between gold and amine terminated 5-aGNRs. 6 However, in the case of 1,10-phenanthroline anchors, with weaker N-Au bonds due to the sp 2 hybridization of N, the inclusion of ASIC displays an undesirable effect.…”