Modeling anisotropic atomic vibrations in diffusive molecular dynamics of magnesium hydride

The coupled diffusion and deformation characterizing diffusive processes on the nanoscale provide significant challenges to many simulation methods due to the combination of fast atomic vibrations and slow diffusion. Diffusive molecular dynamics (DMD) models such processes by a scale separation modeling the thermal vibrations as a spatial position probability distribution and diffusion as atom sites with variable concentrations, which evolve based on kinetic equations. This study introduces a novel type of fully anisotropic spatial probability distribution to improve the approximations for atom sites with anisotropic potential energy wells, e.g. close to surfaces or lattice defects and atoms in lattices with a relatively high degree of intrinsic anisotropy. A comparative study between the classic isotropic and newly introduced anisotropic probability distributions is conducted for the case of magnesium hydride with molecular dynamics simulations using the same interatomic potential serving as reference solution. Tests range from lattice and elastic constants of perfect crystals to more complex cases like the bending of nanobeams and reveal previously unreported shortcomings of isotropic DMD, leading to a loss of lattice symmetry and nonphysical behavior. The results obtained using anisotropic shape functions avoid this behavior and follow the reference solution significantly better while maintaining comparable computational effort. This confirms the requirement for DMD to take anisotropic vibrations into account when simulating magnesium hydride and other systems with anisotropic atom environments.

Subjects

diffusive molecular dynamics

mean field approximation

long-time atomistic simulation / time-scale bridging

non-equilibrium statistical mechanics

anisotropic atomic vibrations

DDC Class

539: Matter; Molecular Physics; Atomic and Nuclear physics; Radiation; Quantum Physics

518: Numerical Analysis

540: Chemistry

Lizenz

https://creativecommons.org/licenses/by/4.0/

Publication version

publishedVersion

Name

Schäfer_2026_Modelling_Simul._Mater._Sci._Eng._34_075014.pdf

Type

Main Article

Size

1.4 MB

Format

Adobe PDF

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Modeling anisotropic atomic vibrations in diffusive molecular dynamics of magnesium hydride