2D vs. 3D titanium dioxide: Role of dispersion interactions

Dispersion-corrected DFT (DFT-D2 and DFT-D3) and van der Waals density functional (vdW-DF) calculations are performed on TiO2, taking in consideration structures common in the nanoscale, viz. two-dimensional lepidocrocite-like (LL) sheets as well as the rutile, brookite, anatase, and B polymorphs. Dispersion effects, which are of marginal importance when comparing ‘monolithic’ polymorphs, are stronger when the comparison is extended to LL structures. We find that, on one hand, LL sheets are less stable than previously estimated; on the other, stacking interactions in LL multilayers, though significant, are rather weak. Overall, these findings explain the reluctance of LL-TiO2 to form ordered stacks.