It was noted that, in a recent article, Hallil et al. had presented 2 empirical variable-charge models for TiO2. Both models were based upon the charge equilibration scheme, which the present authors had shown to be inappropriate for this system due to charge shielding and the subsequent suppression of electrostatic forces. It was therefore questionable whether the extensions proposed by Hallil et al. provided transferability beyond that available with conventional partial charge models. It was recommend that Hallil et al. should test their method using other TixOy systems in order to evaluate its utility.

Comment on “Use of a Variable-Charge Interatomic Potential for Atomistic Simulations of Bulk, Oxygen Vacancies, and Surfaces of Rutile TiO2. Thomas, B.S., Marks, N.A.: Physical Review B, 2007, 76[16], 167401