Provably unconditionally stable, second-order time-accurate, mixed variational methods for phase-field models

We introduce provably unconditionally stable mixed variational methods for phasefield models. Our formulation is based on a mixed finite element method for space discretization and a new second-order accurate time integration algorithm. The fully-discrete formulation inherits the main characteristics of conserved phase dynamics, namely, mass conservation and nonlinear stability with respect to the free energy. We illustrate the theory with the Cahn-Hilliard equation, but our method may be applied to other phase-field models. We also propose an adaptive timestepping version of the new time integration method. We present some numerical examples that show the accuracy, stability and robustness of the new method.