Range separated hybrid density functional study of organic dye sensitizers on anatase TiO2_2 nanowires

The adsorption of organic molecules coumarin and the donor-$\pi$-acceptor type tetrahydroquinoline (C2-1) on anatase (101) and (001) nanowires have been investigated using screened Coulomb hybrid density functional theory calculations. While coumarin forms single bond with the nanowire surface, C2-1 additionally exhibits bidentate mode giving rise to much stronger adsorption energies. Nonlinear solvation effects on the binding characteristics of the dye chromophores on the nanowire facets have also been examined. These two dye sensitizers show different electronic charge distributions for the highest occupied and the lowest unoccupied molecular states. We studied the electronic structures in terms of the positions of the band edges and adsorbate related band gap states and their effect on the absorption spectra of the dye-nanowire combined systems. These findings were interpreted and discussed from the view point of better light harvesting and charge separation as well as in relation to more efficient charge carrier injection into the semiconductor nanowire.Comment: 8 pages, 4 figures, and 1 tabl

JDFTx: software for joint density-functional theory

Density-functional theory (DFT) has revolutionized computational prediction of atomic-scale properties from first principles in physics, chemistry and materials science. Continuing development of new methods is necessary for accurate predictions of new classes of materials and properties, and for connecting to nano- and mesoscale properties using coarse-grained theories. JDFTx is a fully-featured open-source electronic DFT software designed specifically to facilitate rapid development of new theories, models and algorithms. Using an algebraic formulation as an abstraction layer, compact C++11 code automatically performs well on diverse hardware including GPUs. This code hosts the development of joint density-functional theory (JDFT) that combines electronic DFT with classical DFT and continuum models of liquids for first-principles calculations of solvated and electrochemical systems. In addition, the modular nature of the code makes it easy to extend and interface with, facilitating the development of multi-scale toolkits that connect to ab initio calculations, e.g. photo-excited carrier dynamics combining electron and phonon calculations with electromagnetic simulations.Comment: 9 pages, 3 figures, 2 code listing

Dc-switchable and single-nanocrystal-addressable coherent population transfer

Achieving coherent population transfer in the solid-state is challenging compared to atomic systems due to closely spaced electronic states and fast decoherence. Here, within an atomistic pseudopotential theory, we offer recipes for the stimulated Raman adiabatic passage in embedded silicon and germanium nanocrystals. The transfer efficiency spectra display characteristic Fano resonances. By exploiting the Stark effect, we predict that transfer can be switched off with a dc voltage. As the population transfer is highly sensitive to structural variations, with a choice of a sufficiently small two-photon detuning bandwidth, it can be harnessed for addressing individual nanocrystals within an ensemble. © 2010 American Institute of Physics