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To assist the design of novel, highly efficient molecular junctions, a deep understanding of the precise charge transport mechanisms through these devices is of prime importance. In the present contribution, we describe a procedure to investigate spatially-resolved electron transport through a nanojunction from first principles, at the example of a nitro-substituted oligo-(phenylene ethynylene) covalently bound to graphene nanoribbon leads. Recently, we demonstrated that the conductivity of this single-molecule-graphene-nanoribbon junction can be switched quantitatively and reversibly upon application of a static electric field in a top gate position, in the spirit of a traditional field effect transistor [J. Phys. Chem. C, 2016, 120, 28808-28819]. The propensity of the central oligomer unit to align with the external field was found to induce a damped rotational motion and to cause an interruption of the conjugated $\pi$-system, thereby drastically reducing the conductance through the nanojunction. In the current work, we use the driven Liouville-von-Neumann (DLvN) approach for time-dependent electronic transport calculations to simulate the electronic current dynamics under time-dependent potential biases for the two logical states of the nanojunction. Our quantum dynamical simulations rely on a novel localization procedure using an orthonormal set of molecular orbitals obtained from a standard density functional theory calculation to generate a localized representation for the different parts of the molecular junction. The transparent DLvN formalism allows us to directly access the density matrix and to reconstruct the time-dependent electronic current density, unraveling unique mechanistic details of the electron transport.

Graphene pseudohalides are natural candidates for use in molecular sensing due to their greater chemical activity as compared to both graphene halides and pristine graphene. Though their study is still in its infancy, being hindered until recently by the unavailability of both selective and efficient procedures for their synthesis, they promise to considerably widen the application potential of chemically modified graphenes. Herein, we employ vdW-DFT to study the structural and electronic properties of two selected graphene pseudohalides namely cyanographone and isocyanographone and investigate the potential use of the latter as a chemical sensor via electron transport calculations.

Using both DFT as well as $G_0W_0$ calculations, we investigate static and dynamic effects on the phosphorene band gap upon deposition and encapsulation on/in BN multilayers. We demonstrate how competing long- and short-range effects cause the phosphorene band gap to increase at low P - BN interlayer spacings, while the band gap is found to drop below that of isolated phosphorene in the BN/P bilayer at intermediate distances around 4 \AA. Subsequent stacking of BN layers, i.e. BN/BN/P and BN/BN/BN/P is found to have a negligible effect at the DFT level while at the $G_0W_0$ increased screening lowers the band gap as compared to the BN/P bilayer. Encapsulation between two BN layer is found to increase the phosphorene band gap by a value approximately twice that observed when going from freestanding phosphorene to BN/P. We further investigate the use of the $\rm{GLLB-SC}$ functional as a starting point for $G_0W_0$ calculations showing it to, in the case of phosphorene, yield results close to those obtained from $GW_0@\rm{PBE}$ calculations.

While halogenation of graphene presents a fascinating avenue to the construction of a chemically and physically diverse class of systems, their application in photovoltaics has been hindered by often prohibitively large optical gaps. Herein we study the effects of partial bromination and chlorination on the structure and optoelectronic properties of both graphane and fluorographene. We find brominated and chlorinated fluorographene derivatives to be as stable as graphane making them likely to be durable even at elevated temperatures. A detailed investigation of the systems band structure reveals significant 1D localization of the charge carriers as well as strongly electron-hole asymmetric effective masses. Lastly using $G_0W_0$ and BSE, we investigate the optical adsorption spectra of the aforementioned materials whose first adsorption peak is shown to lie close to the optimal peak position for photovoltaic applications ($\approx 1.5$ eV).