VacHopPy: A Python package for vacancy hopping analysis based on ab initio molecular dynamics simulations

Abstract: Multiscale modeling, which integrates material properties from ab initio calculations into device-scale models, is a promising approach for optimizing semiconductor devices. However, a key challenge remains: while ab initio methods yield diffusion parameters specific to individual migration paths, device models require a single set of effective parameters that capture overall diffusion. To bridge this gap, we present VacHopPy an open-source Python package for vacancy hopping analysis based on ab initio molecular dynamics (AIMD). VacHopPy extracts an effective set of parameters for vacancy hopping: hopping distance, hopping barrier, number of effective paths, correlation factor, and jump attempt frequency, by statistically integrating thermodynamic, kinetic, and geometric contributions across all hopping paths. It also offers tools for tracking vacancy trajectories and for detecting phase transitions in AIMD simulations. The applicability of VacHopPy is demonstrated in three materials: face-centered cubic Al, rutile TiO2, and monoclinic HfO2. The effective parameters accurately reflect temperature-dependent diffusion behavior and show good agreement with previous experimental observations. Expressed in a simplified form suitable for device models, these parameters remain valid across a broad temperature range spanning several hundred Kelvins. Furthermore, our findings highlight the critical role of anisotropic thermal vibrations in overall diffusion, a factor frequently overlooked in other frameworks but inherently considered in VacHopPy. Overall, VacHopPy provides a robust framework for bridging atomistic and device-scale models, enabling more reliable multiscale simulations.