  This paper introduces the MeshAC package, which generates three-dimensional
adaptive meshes tailored for the efficient and robust implementation of
multiscale coupling methods. While Delaunay triangulation is commonly used for
mesh generation across the entire computational domain, generating meshes for
multiscale coupling methods is more challenging due to intrinsic discrete
structures such as defects, and the need to match these structures to the
continuum domain at the interface. The MeshAC package tackles these challenges
by generating meshes that align with fine-level discrete structures. It also
incorporates localized modification and reconstruction operations specifically
designed for interfaces. These enhancements improve both the implementation
efficiency and the quality of the coupled mesh. Furthermore, MeshAC introduces
a novel adaptive feature that utilizes gradient-based a posteriori error
estimation, which automatically adjusts the atomistic region and continuum
mesh, ensuring an optimal balance between accuracy and efficiency. This package
can be directly applied to the geometry optimization problems of a/c coupling
in static mechanics, with potential extensions to many other scenarios. Its
capabilities are demonstrated for complex material defects, including straight
edge dislocation in BCC W and double voids in FCC Cu. These results suggest
that MeshAC can be a valuable tool for researchers and practitioners in
computational mechanics.
