Crystallization of hard spheres within ellipsoidal confinement

Using event-driven molecular dynamics simulations, we investigate the crystallization of hard spheres confined within ellipsoidal cavities and find that the curvature anisotropy of the confining boundary governs both nucleation and growth dynamics. Crystallization preferentially initiates at low-curvature regions and propagates inward. In prolate ellipsoids, multiple nuclei emerge along the equatorial plane and grow into several misoriented crystalline domains, whereas in oblate ellipsoids, crystallization starts at the poles and results in a nearly monocrystalline structure. The free energy of nucleation scales linearly with cluster size, reflecting a surface-dominated growth mechanism, and the free-energy penalty per particle follows a universal power-law dependence on the Gaussian curvature. The distribution of lattice defects on the curved surface is consistent with the anisotropic crystallization inside the cavity, revealing that curvature-induced defect localization controls the symmetry breaking of confined crystallization.