A quantum mechanical study of TiCl₃α, β and γ crystal phases: Geometry, electronic structure and magnetism

The electronic structure of different magnetic states of α, β and γ modifications of TiCl₃ has been computed employing the density functional theory with periodic boundary conditions and localized Gaussian basis sets. The analysis of the density of the electronic states (DOS) and of the spin density makes it possible to classify these halides as Mott-Hubbard insulators, where the band gap appears a result of large on-site Coulomb interaction. For each crystalline phase, the relative stability of different magnetic states has been analyzed in terms of exchange mechanisms. The electronic population data along with the spin density maps support the assumption of a d¹ Titanium ion in a distorted octahedral crystal field, notwithstanding the not fully ionic character of TiCl₃ modifications. Dispersion forces are particularly important for this material: a classical correction (of the type f(R)/R⁶) has been added to the DFT energies and gradients, providing a good agreement with structural data.