Threshold displacement energies in rutile TiO2: A molecular dynamics simulation study

Threshold displacement energies are determined for Ti and O in rutile TiO2 using molecular dynamics simulations with an empirical model. The simulations involve the introduction of a primary knock-on atom (PKA) with a range of energies (30-150 eV) in various crystallographic directions at 160 K. We observe the formation of stable Frenkel defects, as well as defect recovery via low-energy interstitial migration mechanisms. The latter causes significant statistical variation between simulation outcomes, which leads to the definition of a defect formation probability. This probability is characterized as a function of PKA energy in order to define the threshold displacement energy and compare with experimental results. Using a probability of 10%, the average threshold displacement energy is around 40 eV for oxygen (comparable to experiment) and 105 eV for titanium. Using a probability of 50%, the values are 65 eV and 130 eV respectively, which may be more appropriate for use in TRIM calculations. In addition, we run a parallel set of calculations using a second empirical model, finding that the detailed results are highly model-dependent, particularly the oxygen defect structures and energies, which are compared to new ab initio data.