Tensor gradient flow with quasi-entropy for smectic liquid crystals and discretizations keeping coupled physical constraints
For researchers in liquid crystal modeling and numerical analysis, this work provides a thermodynamically consistent framework and structure-preserving discretization for smectic phases, though it is an incremental extension of existing gradient flow and entropy methods.
The authors constructed a gradient flow for smectic liquid crystals using a quasi-entropy term that imposes coupled constraints between concentration and tensor fields, and developed numerical schemes that preserve these constraints and energy dissipation. Numerical results demonstrate efficiency, robustness, and observation of novel defect configurations.
A gradient flow for the concentration and a $2\times 2$ tensor is constructed to describe smectic liquid crystals. The free energy consists of the entropy term and interaction term involving squared second order spatial derivatives. The entropy term incorporates the concentration in the quasi-entropy originally proposed for the tensor only, which is a strictly convex and lower semicontinuous function imposing coupled constraints between the concentration and the tensor. An evolution equation for the boundary normal derivative of the concentration is proposed in addition to the equations for the concentration and the tensor, giving an energy dissipation system. Numerical schemes are designed with emphases on using the entropy term to keep the coupled constraints, and the discretization of the boundary normal derivatives satisfying summation by parts. Existence, uniqueness, energy dissipation and error estimates are established. Numerical results indicate the efficiency and robustness of the scheme. Configurations of defects different from other layer structures are observed.