Modelling and Simulation in Materials Science and Engineering

Schäfer, Philipp M; Cyron, Christian J

doi: 10.1088/1361-651x/ae6ba2pmid: N/A

Diffusive processes on the nanoscale, characterized by coupled diffusion and deformation, pose significant challenges for the assessment using conventional simulation methods due to their long time scales. Diffusive molecular dynamics (DMD) models such diffusive processes by optimizing positions and vibration frequencies of atom sites with variable concentrations evolving based on kinetic equations. Despite its various applications, validation studies for this method still remain limited due to a lack of suitable reference solutions and an absence of comparisons among different kinetic equations. This paper aims to fill these gaps by directly comparing DMD, utilizing different kinetic equations, with traditional molecular dynamics (MD) for the case of palladium hydride on thermal and diffusive time scales. Employing the same interatomic potential in both methods helps to isolate errors attributed solely to the assumptions inherent in DMD. The simulations conducted, which include measurements of lattice and elastic constants as well as surface diffusion and hydration processes of a nanocube, reveal that although DMD generally captures the trends observed in the reference solutions quite well, it exhibits non-negligible quantitative discrepancies in both static properties and diffusive behaviors. Among the tested kinetic equations, a linear approach and a master equation depending on vacancy formation energy showed the best agreement with the reference solutions. This study underscores the necessity for further refinement of DMD like enhanced kinetic equations that account for local environmental factors and improved mean-field approximations better suited to complex interatomic potentials. Given the significant advantages DMD offers as a method, efforts in this direction are doubtlessly an interesting avenue for future research.