Simulation of titanium metal/titanium dioxide etching with chlorine and hydrogen chloride gases using the ReaxFF reactive force field

In this study, a new ReaxFF reactive force field has been developed to describe reactions in Ti/O/Cl/H materials. This force field was applied to etching simulations for titanium metal and titanium dioxide with chlorine and hydrogen chloride gases. The ReaxFF force field parameters are fitted against a quantum mechanical (QM) training set containing structures and energies related to bond dissociations, angle and dihedral distortions, and reactions between titanium and chlorine gases as well as heats of formation of TiCl_x crystals. These newly developed Ti-Cl force field parameters were combined with a recently developed Ti-O-H force field. ReaxFF accurately reproduces the QM training set for structures and energetics of small clusters and TiCl _x crystals. In the etching simulations, titanium and titanium dioxide slab models with chlorine and hydrogen chloride gases were used in molecular dynamics simulations. The etching ratio between HCl and Cl₂ are compared to experimental results, and satisfactory results are obtained, indicating that this ReaxFF extension provides a useful tool for studying the atomistic-scale details of the etching process.