Assessing density functionals for the prediction of thermochemistry of Ti-O-Cl species

Titanium dioxide (TiO2) nanoparticles are widely used in contaminant remediation, photocatalysis, and solar cell manufacturing. The low-cost production of TiO2 nanoparticles via the combustion of titanium tetrachloride (TiCl4) in oxygen is thus an important industrial process. To accurately model the flame synthesis of TiO2 nanoparticles, reliable thermodynamic data of Ti-O-Cl species are indispensable but often unavailable. We therefore carried out benchmark calculations, using the left-eigenstate completely renormalized singles, doubles, and perturbative triples (CR-CC(2,3), aka CR-CCL) method with the cc-pVTZ basis set, to obtain the equilibrium structures and vibrational frequencies of selected Ti-O-Cl species; we then performed single-point CCSD(T)/aug-cc-pVLZ (L = 3-5) calculations to extrapolate the CCSD(T)/CBS energies. After analyzing the experimental and calculated enthalpy of selected Ti-O-Cl species, the standard enthalpy of formation of the TiOCl2 molecule is determined to be -600.5 kJ/mol at 298 K. The standard enthalpy of all other Ti-O-Cl species are determined accordingly. Finally, we assessed the accuracy of 42 popular density functionals for the Ti-O-Cl species. Among these assessed functionals, the B98 functional, tightly followed by B97-1 and B3LYP, exhibits the best overall performance in the prediction of the thermochemistry of the Ti-O-Cl species