Multistability for nematic liquid crystals in cuboids with degenerate planar boundary conditions

Shi, Baoming and Han, Yucen and Majumdar, Apala and Zhang, Lei (2024) Multistability for nematic liquid crystals in cuboids with degenerate planar boundary conditions. SIAM Journal on Applied Mathematics, 84 (2). pp. 756-781. ISSN 0036-1399 (https://doi.org/10.1137/23m1604606)

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Abstract

We study nematic configurations within three-dimensional (3D) cuboids, with planar degenerate boundary conditions on the cuboid faces, in the Landau–de Gennes framework. There are two geometry-dependent variables: the edge length of the square cross-section, λ, and the parameter h, which is a measure of the cuboid height. Theoretically, we prove the existence and uniqueness of the global minimizer with a small enough cuboid size. We develop a new numerical scheme for the high-index saddle dynamics to deal with the surface energies. We report on a plethora of (meta)stable states, and their dependence on h and λ, and in particular how the 3D states are connected with their two-dimensional counterparts on squares and rectangles. Notably, we find families of almost uniaxial stable states constructed from the topological classification of tangent unit-vector fields and study transition pathways between them. We also provide a phase diagram of competing (meta)stable states as a function of λ and h.