Dissociation of water on the surface of galena (PbS): A comparison of periodic and cluster models

Exploiting the locality of periodic subsystem density-functional theory: efficient sampling of the Brillouin zone

In order to approximately satisfy the Bloch theorem, simulations of complex materials involving periodic systems are made n(k) times more complex by the need to sample the first Brillouin zone at n(k) points. By combining ideas from Kohn-Sham density-functional theory (DFT) and orbital-free DFT, for which no sampling is needed due to the absence of waves, subsystem DFT offers an interesting middle ground capable of sizable theoretical speedups against Kohn-Sham DFT. By splitting the supersystem into interacting subsystems, and mapping their quantum problem onto separate auxiliary Kohn-Sham systems, subsystem DFT allows an optimal topical sampling of the Brillouin zone. We elucidate this concept with two proof of principle simulations: a water bilayer on Pt[1 1 1]; and a complex system relevant to catalysis-a thiophene molecule physisorbed on a molybdenum sulfide monolayer deposited on top of an α-alumina support. For the latter system, a speedup of 300% is achieved against the subsystem DTF reference by using an optimized Brillouin zone sampling (600% against KS-DFT).

Effects of reduced dimensionality on the electronic structure and defect chemistry of semiconducting hybrid organic–inorganic PbS solids

The combination of inorganic and organic frameworks to produce crystalline hybrid semiconductors offers a pathway for obtaining novel photovoltaic and optoelectronic materials. Taking an archetypal binary semiconductor, PbS (galena), we investigate the electronic effects of the reduced dimensionality in the PbS framework on transition from bulk PbS to three-dimensional and one-dimensional hybrid inorganic–organic networks. Analysis of density functional theory calculations reveals the substantial contribution of the organic (benzenehexathiol derivates) to the band-edge states. Implications for intrinsic defect formation and potential application in solar cell devices are discussed, as well as future design pathways for engineering the electronic properties of this new class of hybrid metal–organic framework.