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Proton-transfer reactions in imidazole molecules confined in the metal-organic framework MIL-53(Al) were studied by means of Born-Oppenheimer molecular-dynamics simulations employing the density-functional tight-binding method. The statistical analysis of the trajectories revealed an essential impact of the framework on the orientation of the molecules in its channels and, thus, on the hydrogen-bond network. The one-dimensional hydrogen-bond network is one reason for faster reorientation dynamics compared to liquid imidazole. A lifetime in the order of 100 fs could be attributed to the proton-transfer transition state, a Zundel-like ion, and the combined imidazole@MIL-53(Al) system exhibited shorter times between hopping events compared to the liquid phase. This goes along with experimental findings of enhanced proton conductivity in this system. [ABSTRACT FROM AUTHOR]

Using a parameterized density-functional method we have studied the structural and electronic properties of different II–VI and III–V semiconductor clusters. We studied finite parts of the zincblende and wurtzite crystal structure for CdS, CdSe, InP, and ZnO and allowed the structures to relax to the closest total-energy minimum. Both stoichiometric and non-stoichiometric naked clusters were considered. We found (i) that the relative stability of the zincblende- and the wurtzite-derived clusters depends on the size of the structure, (ii) that the total-energy per atom is a non-smooth function of the size, and (iii) a correlation between the size of the HOMO–LUMO bandgap and the stability of the cluster. The implications of these results for the experimental analysis of the size distributions are discussed. [Copyright &y& Elsevier]