Speed-dependent adaptive partitioning in QM/MM MD simulations of displacement damage in solid-state systems

Solids undergo displacement damage (DD) when interacting with energetic particles, which may happen during the fabrication of semiconductor devices, in harsh environments and in certain analysis techniques. Simulations of DD generation are usually carried out using classical molecular dynamics (MD), but classical MD does not account for all the effects in DD, as demonstrated by ab initio calculations of model systems in the literature. A complete ab initio simulation of DD generation is impractical due to the large number of atoms involved. In my previous paper [Yang, Phys. Chem. Chem. Phys., 2020, 22, 19307], I developed an adaptive-center (AC) method for the adaptive-partitioning (AP) of quantum mechanics/molecular mechanics (QM/MM) simulations, allowing the active region centers and the QM/MM partition to be determined on-the-fly for energy-conserving AP-QM/MM methods. I demonstrated that the AC-AP-QM/MM is applicable to the simulation of DD generation, so that the active regions can be treated using an ab initio method. The AC method could not be used to identify the fast-moving recoil ions in DD generation as active region centers, however, and the accuracy is negatively affected by the rapid change in the QM/MM partition of the system. In this paper, I extend the AC method and develop a speed-dependent adaptive-center (SDAC) method for accurate AP-QM/MM simulations of DD. The SDAC method is applicable to general problems with speed-dependent active regions, and is compatible with all existing energy-conserving partitioning-by-distance AP-QM/MM methods. The artifact due to the speed-dependent potential energy surface can be made small by choosing suitable criteria. I demonstrate the SDAC method by simulations of DD generation in bulk silicon.