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The primary particles of silica aerogels resulting from three different mixtures of precursors – 50% tetramethylorthosilicate (TMOS)/50% vinyltrimethoxysilane (VMTS); 50% tetraethylorthosilicate (TEOS)/50% aminopropyltriethoxysilane and 50% TEOS/50% glycidylpropoxi – as well as aerogels of pure TMOS and VTMS, have been studied by quantum mechanics density functional theory calculations (DFT), at the B3LYP/6-311+G(d,p) level of theory). Thermo-chemical calculations have indicated that cage structures are the most favored for all materials, followed by other species (linear and cyclic) with high degrees of condensation. A vibration mode analysis based on a numerical model fitted to experimental infrared spectra, has allowed the identification of the most representative silica clusters for all the materials studied. The resulting theoretical spectra were close to their experimental counterparts. Analysis of calculated and experimental 29Si-NMR spectral data generally corroborated the derived model.

The formation and migration energies of interstitial hydrogen in rutile TiO2 are obtained from first principles calculations. The computational approach was based on density functional theory with a semilocal generalised-gradient approximation functional, supplemented with an on-site Hubbard term to account for correlation among the Ti 3d electrons. Charge-transition levels are calculated and compared to previous theoretical studies. The donor character of hydrogen is examined in depth, focusing in particular on the tendency to form polaron-like configurations with the unpaired electron trapped at nearby titanium ions. Distinct minimum-energy paths of hydrogen migration and associated energy barriers were determined by the nudged elastic-band method. The present findings show clearly the strong anisotropy in the energy barriers for migration within the open c channels as opposed to migration crossing adjacent channels of the rutile lattice. For the rate-limiting step which leads to macroscopic diffusion along the c axis the corresponding rate and diffusion coefficient were also determined from transition-state theory. The results are discussed in connection to existing measurements of hydrogen diffusion and recent findings from electron paramagnetic resonance, electron-nuclear double resonance and muonium spectroscopies that probed the spatial localization of the electron spin.

The geometry, energy and stretching frequency of carbon monoxide on the rutile TiO2(110) surface for coverages between 0.125 and 1.5 ML are investigated by means of density functional theory calculations. Four different approaches were considered, namely, the PBE exchange–correlation functional and the PBE-D2, vdW-DF and vdW-DF2 methods incorporating van der Waals dispersion interactions of different theoretical complexity and empiricism. It is found that upon the increase of the surface coverage, the adsorption becomes less favorable due to lateral destabilizing interactions between adsorbed molecules. The preferred geometry for CO changes from an upright configuration at 0.125 ML to tilted configurations at 1.5 ML and the tilting of the C–O axis from the surface normal increases with the increase of the surface coverage. At 1 ML, all computational approaches predict alternate tilted configurations which contradict the interpretation of recent experimental infrared reflection–absorption spectroscopic findings suggesting upright CO geometries. Encouragingly, a very good agreement between calculated and experimental shifts of the C–O stretching frequency of adsorbed CO at different coverages with respect to gaseous CO species was reached.

This article reviews the different density functional theory (DFT) methods available in the literature for dealing with dispersion interactions and recent applications of DFT approaches including van der Waals corrections in the study of the interaction of atoms and molecules with several different surfaces. Focus is given to the interaction of atoms and molecules with metal, metal oxide and graphite surfaces or more complex systems. It will be shown that DFT approaches including van der Waals corrections present significant advances over standard exchange-correlation functionals for treating systems dominated by weak interactions.

This study reports a combined experimental and theoretical study of the solid-state polymorphism of the anticancer agent cisplatin. A complete assignment was performed for the inelastic neutron scattering (INS) and Raman spectra collected simultaneously for cisplatin, at different temperatures, with a view to obtain reliable and definitive evidence of the relative thermal stability of its α and β polymorphic species. A marked temperature-dependent hysteresis was observed, as previously reported in the literature. Theoretical calculations were carried out at the density functional theory level, using a plane-wave basis set approach and pseudopotentials. A detailed comparison with the experimental Raman and INS data showed that the α polymorph is present at the lowest temperatures, whereas the β form occurs near room temperature. Furthermore, regions of coexistence of both forms are identified, which depend on the working mode (heating or cooling). These findings imply that Raman spectroscopy allows clear identification of the α and β polymorphs at a given temperature and can unambiguously discriminate between them. Elucidation of the polymorphic equilibrium of this widely used anticancer drug is paramount for its pharmaceutical preparation and storage conditions.