The immense potential of colossal permittivity (CP) materials for use in modern microelectronics as well as for high-energy-density storage applications has propelled much recent research and development. Despite the discovery of several new classes of CP materials, the development of such materials with the required high performance is still a highly challenging task. Here, we propose a new electron-pinned, defect-dipole route to ideal CP behaviour, where hopping electrons are localized by designated lattice defect states to generate giant defect-dipoles and result in high-performance CP materials. We present a concrete example, (Nb+In) co-doped TiO₂ rutile, that exhibits a largely temperature- and frequency-independent colossal permittivity (> 10(4)) as well as a low dielectric loss (mostly < 0.05) over a very broad temperature range from 80 to 450 K. A systematic defect analysis coupled with density functional theory modelling suggests that 'triangular' In₂(3+)Vo(••)Ti(3+) and 'diamond' shaped Nb₂(5+)Ti(3+)A(Ti) (A = Ti(3+)/In(3+)/Ti(4+)) defect complexes are strongly correlated, giving rise to large defect-dipole clusters containing highly localized electrons that are together responsible for the excellent CP properties observed in co-doped TiO₂. This combined experimental and theoretical work opens up a promising feasible route to the systematic development of new high-performance CP materials via defect engineering.

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While the majority of the photochemical states and pathways related to the biological capture of solar energy are now well understood and provide paradigms for artificial device design, additional low-energy states have been discovered in many systems with obscure origins and significance. However, as low-energy states are naively expected to be critical to function, these observations pose important challenges. A review of known properties of low energy states covering eight photochemical systems, and options for their interpretation, are presented. A concerted experimental and theoretical research strategy is suggested and outlined, this being aimed at providing a fully comprehensive understanding.

Molecular dynamics simulations of hydrogen-containing type-sII clathrate hydrate slabs have been performed. A range of water-water interaction potentials were tested. Three potentials that yield water ice melting points close to 273 K gave very different clathrate stabilities. The TIP5P potential was found to give the closest match to experimentally observed clathrate stabilities. Using this potential, we investigated molecular hydrogen mobility within the clathrate. It was found that hydrogen molecules within the large clathrate cages were highly mobile, migrating rapidly from cage to cage and giving instantaneous cage occupations of up to six hydrogen molecules per cage. Self-diffusion coefficients for hydrogen migration were calculated and found to obey an Arrhenius relation. Hydrogen in the small cages was not mobile on the time scale of the simulations. Simulations including the known promoter molecule tetrahydrofuran demonstrated enhanced stability of the clathrate, consistent with experimental data.