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Inthis study, a new ReaxFF reactive force field has been developed todescribe reactions in Ti/O/Cl/H materials. This force field was appliedto etching simulations for titanium metal and titanium dioxide withchlorine and hydrogen chloride gases. The ReaxFF force field parametersare fitted against a quantum mechanical (QM) training set containingstructures and energies related to bond dissociations, angle and dihedraldistortions, and reactions between titanium and chlorine gases aswell as heats of formation of TiClxcrystals.These newly developed Ti–Cl force field parameters were combinedwith a recently developed Ti–O–H force field. ReaxFFaccurately reproduces the QM training set for structures and energeticsof small clusters and TiClxcrystals.In the etching simulations, titanium and titanium dioxide slab modelswith chlorine and hydrogen chloride gases were used in molecular dynamicssimulations. The etching ratio between HCl and Cl2arecompared to experimental results, and satisfactory results are obtained,indicating that this ReaxFF extension provides a useful tool for studyingthe atomistic-scale details of the etching process. [ABSTRACT FROM AUTHOR]

A newReaxFF reactive force field has been developed to describereactions in the Ti–O–H system. The ReaxFF force fieldparameters have been fitted to a quantum mechanical (QM) trainingset containing structures and energies related to bond dissociationenergies, angle and dihedral distortions, and reactions between waterand titanium dioxide, as well as experimental crystal structures,heats of formation, and bulk modulus data. Model configurations forthe training set were based on DFT calculations on molecular clustersand periodic systems (both bulk crystals and surfaces). ReaxFF reproducesaccurately the QM training set for structures and energetics of smallclusters. ReaxFF also describes the relative energetics for rutile,brookite, and anatase. The results of ReaxFF match reasonably wellwith those of QM for water binding energies, surface energies, andH2O dissociation energy barriers. To validate this ReaxFFdescription, we have compared its performance against DFT/MD simulationsfor 1 and 3 monolayers of water interacting with a rutile (110) surface.We found agreement within a 10% error between the DFT/MD and ReaxFFwater dissociation levels for both coverages. [ABSTRACT FROM AUTHOR]