Convex Splitting Method for the Calculation of Transition States of Energy Functional
For researchers in computational materials science and PDEs, this provides a more efficient numerical method for finding transition states in phase-field models.
The authors extend the convex splitting method, known for energy stability in gradient flow dynamics, to efficiently compute index-1 saddle points (transition states) of energy functionals. They demonstrate large time step sizes and test on 1D Ginzburg-Landau and 2D Landau-Brazovskii functionals.
Among numerical methods for partial differential equations arising from steepest descent dynamics of energy functionals (e.g., Allen-Cahn and Cahn-Hilliard equations), the convex splitting method is well-known to maintain unconditional energy stability for a large time step size. In this work, we show how to use the convex splitting idea to find transition states, i.e., index-1 saddle points of the same energy functionals. Based on the iterative minimization formulation (IMF) for saddle points (SIAM J. Numer. Anal., vol. 53, p1786, 2015), we introduce the convex splitting method to minimize the auxiliary functional at each cycle of the IMF. We present a general principle of constructing convex splitting forms for these auxiliary functionals and show how to avoid solving nonlinear equations. The new numerical scheme based on the convex splitting method allows for large time step sizes. The new methods are tested for the one dimensional Ginzburg-Landau energy functional in the search of the Allen-Cahn or Cahn-Hilliard types of transition states. We provide the numerical results of transition states for the two dimensional Landau-Brazovskii energy functional for diblock copolymers.