The hydrolysis of titanium tetrachloride (TiCl(4)) to produce titanium dioxide (TiO(2)) nanoparticles has been studied to provide insight into the mechanism for forming these nanoparticles. We provide calculations of the potential energy surfaces, the thermochemistry of the intermediates, and the reaction paths for the initial steps in the hydrolysis of TiCl(4). We assess the role of the titanium oxychlorides (Ti(x)O(y)Cl(z); x = 2-4, y = 1, 3-6, and z = 2, 4, 6) and their viable reaction paths. Using transition-state theory and RRKM theory, we predicted rate constants including the effect of tunneling. Heats of formation at 0 and 298 K are predicted for TiCl(4), TiCl(3)OH, TiOCl(2), TiOClOH, TiCl(2)(OH)(2), TiCl(OH)(3), Ti(OH)(4), and TiO(2) using the CCSD(T) method with correlation consistent basis sets extrapolated to the complete basis set limit and compared with the available experimental data. Clustering energies and heats of formation are calculated for neutral clusters. The calculated heats of formation were used to study condensation reactions that eliminate HCl or H(2)O. The reaction energy is substantially endothermic if more than two HCl molecules are eliminated. The results show that the mechanisms leading to formation of TiO(2) nanoparticles and larger ones are complicated and will have a strong dependence on the experimental conditions.

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energies always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.

Hirshfeld-I charges were implemented in the Crystal code, for periodic calculations with localized atomic basis sets. Some particular features of the present periodic implementation are detailed and discussed by means of selected illustrating examples. In these examples, the Hirshfeld-I charges are somewhere between the Bader and the Mulliken values and closer to the former. The implementation exploits heavily symmetry aspects and is shown to scale linearly with the unit cell dimension.Keywords Hirshfeld Iterative · Periodic calculations · Ab Initio · LCAO To A. Vela for his high human and scientific qualities.

The evolution under pressures up to 65 GPa of structural, elastic and vibrational properties of the katoite hydrogarnet, Ca3Al2(OH)12, is investigated with an ab initio simulation performed at the B3LYP level of theory, by using all-electron basis sets with the Crystal periodic program. The high-symmetry Ia3d phase of katoite, stable under ambient conditions, is shown to be destabilized, as pressure increases, by interactions involving hydrogen atoms and their neighbors which weaken the hydrogen bonding network of the structure. The corresponding thermodynamical instability is revealed by anomalous deviations from regularity of its elastic constants and by numerous imaginary phonon frequencies, up to 50 GPa. Interestingly, as pressure is further increased above 50 GPa, the Ia3d structure is shown to become stable again (all positive phonon frequencies and regular elastic constants). However, present calculations suggest that, above about 15 GPa and up to at least 65 GPa, a phase of I4[combining macron]3d symmetry (a non-centrosymmetric subgroup of Ia3d) becomes more stable than the Ia3d one, being characterized by strengthened hydrogen bonds. At low-pressures (between about 5 GPa and 15 GPa), both phases show some instabilities (more so for I4[combining macron]3d than for Ia3d), thus suggesting either the existence of a third phase or a possible phase transition of second order.