Outcomes of a seminal research (B. Xu and N. J. Tao, Science, 2003, 301, 1221) on the single-molecule junctions primarily based on bipyridine positioned in a solvent have been challenged just lately (S. Y. Quek et al., Nat. Nano, 2009, 4, 230) by implicitly assuming a negligible solvent affect on the molecular transport and by merely contemplating low bias conductance information.
On this paper we display that solvent results on the molecular transport are necessary, and to point out this we focus our consideration on the vitality offset ε(0) of the dominant molecular orbital (LUMO) relative to the electrode Fermi degree.
To estimate the vitality offset ε(0)(sol) from the total I-V curves introduced by Xu and Tao for moist junctions, we resort to the just lately proposed transition voltage spectroscopy (TVS). TVS, which performs a key position within the current evaluation, emphasizes that information past the ohmic conductance regime are wanted to disclose the solvent affect. We present that ε(0)(sol) considerably differs from the vitality offset ε(0)(0)deduced for dry junctions (J. R. Widawsky et al., Nano Lett., 2012, 12, 354).
The current work demonstrates that solvent results on molecular transport are necessary and may be understood quantitatively. Outcomes of ab initio calculations with and with out solvent are reported that excellently clarify the distinction δε(0) = ε(0)(sol)-ε(0)(0). δε(0) = ΔΔG + δΦ + δW may be disentangled in contributions with a transparent bodily content material: solvation energies (ΔΔG), picture fees (δΦ), and work features (δW). Correct analytical formulae for ΔΔG and δΦ are reported, which offer experimentalists with a handy framework to quantify solvent results obviating demanding numerical efforts.
Digital construction calculations with GPAW: a real-space implementation of the projector augmented-wave technique
Digital construction calculations have grow to be an indispensable software in lots of areas of supplies science and quantum chemistry. Despite the fact that the Kohn-Sham formulation of the density-functional concept (DFT) simplifies the many-body downside considerably, one continues to be confronted with a number of numerical challenges.
On this article we current the projector augmented-wave (PAW) technique as carried out within the GPAW program bundle utilizing a uniform real-space grid illustration of the digital wavefunctions.
In comparison with extra conventional airplane wave or localized foundation set approaches, real-space grids supply a number of benefits, most notably good computational scalability and systematic convergence properties. Nonetheless, as a singular characteristic GPAW additionally facilitates a localized atomic-orbital foundation set along with the grid.
The environment friendly atomic foundation set is complementary to the extra correct grid, and the likelihood to seamlessly swap between the 2 representations offers nice flexibility. Whereas DFT permits one to review floor state properties, time-dependent density-functional concept (TDDFT) offers entry to the excited states.
We’ve carried out the 2 frequent formulations of TDDFT, particularly the linear-response and the time propagation schemes. Electron transport calculations beneath finite-bias situations may be carried out with GPAW utilizing non-equilibrium Inexperienced features and the localized foundation set.
Along with the essential options of the real-space PAW technique, we additionally describe the implementation of chosen exchange-correlation functionals, parallelization schemes, ΔSCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals.